System for manufacturing reinforced three-zone microporous membrane

ABSTRACT

Systems and methods for the manufacture of reinforced, three-zone, microporous phase inversion membrane having any one of a plurality of different possible pore sizes in any of the three zones from at least a single mother dope batch is disclosed. The systems and methods include formulating at least a single mother batch of dope in a vessel preferably maximizing the non-solvent to solvent ratio for a given weight percentage of polymer for use in a microporous phase inversion membrane production operation to produce three-zone phase inversion membranes having one of a plurality of different predetermined pore sizes in any or all of the three zones. The at least one mother dope batch is controllably formulated in at least one vessel such that the temperature of the dope does not exceed a predetermined maximum mixing temperature and is maintained at a relatively low temperature (lower than the mixing temperature) suitable for storage.

RELATED APPLICATIONS

This application is related to commonly owned U.S. Provisional PatentApplication Ser. No. 60/043,181, filed Apr. 11, 1997, of Meyering etal., the disclosure of which is herein incorporated by reference and isa continuation-in-part of U.S. patent application Ser. No. 09/022,295,filed Feb. 11, 1998, of Meyering et al., now U.S. Pat. No. 6,056,529issued May 2, 2000 and Ser. No. 09/412,494 filed Oct. 9, 1999 now U.S.Pat. No. 6,267,916 issued Jul. 31, 2001, U.S. patent application Ser.No. 09/040,979, filed Mar. 18, 1998, of Meyering et al., now U.S. Pat.No. 6,264,044 issued Jul. 24, 2001 and U.S. patent application Ser. No.09/040,816, filed Mar. 18, 1998, of Vining et al., now U.S. Pat. No.6,090,441 issued Jul. 18, 2000, and U.S. Provisional Patent ApplicationSer. No. 60/123,459 of Meyering et al., filed Mar. 9, 1999, thedisclosure of each is herein incorporated by reference.

BACKGROUND OF THE INVENTION

The present application, as presently envisioned, relates to systems andmethods for the manufacture of continuous, three-zone reinforced,geometrically symmetrical, microporous membranes having three distinctpore zones, each zone being formed from at least one of a plurality ofdifferent pore size producing dopes, more particularly to systems andmethods for the continuous manufacture of continuous, reinforced,three-zone microporous membrane including a scrim having two sides atleast substantially encapsulated within any one of a plurality pore sizeproducing first dopes produced from a single mother dope batch and atleast one additional dope presently preferably produced from the samesingle mother dope batch coated onto each side of the substantiallyencapsulated scrim prior to the first dope being quenched and, mostparticularly, to systems and methods for the manufacture of ageometrically symmetric, continuous, reinforced membrane having threedistinct pore zones including a scrim at least substantially andpreferably, completely encapsulated by a relatively large pore sizemiddle zone produced from any one of a plurality of different pore sizedopes, which may be continuously produced from a single mother dopebatch and two outer zones, one on each side of the middle zone, at leastone of the three zones having a pore size at least about twenty (20%)percent greater than at least one of the other zones.

Microporous phase inversion membranes are well known in the art.Microporous phase inversion membranes are porous solids which containmicroporous interconnecting passages that extend from one surface to theother. These passages provide tortuous tunnels or paths through whichthe liquid which is being filtered must pass. The particles contained inthe liquid passing through a microporous phase inversion membrane becometrapped on or in the membrane structure effecting filtration. A slightpressure, generally in the range of about one half (0.5) to about fifty(50) psig (pounds per square inch gauge) is used to force fluid throughthe microporous phase inversion membrane. The particles in the liquidthat are larger than the pores are either prevented from entering themembrane or are trapped within the membrane pores and some particlesthat are smaller than the pores are also trapped or absorbed into themembrane pore structure within the pore tortuous path. The liquid andsome particles smaller than the pores of the membrane pass through.Thus, a microporous phase inversion membrane prevents particles of acertain size or larger from passing through it, while at the same timepermitting liquid and some particles smaller than that certain size topass through. Microporous phase inversion membranes have the ability toretain particles in the size range of from about 0.01 or smaller toabout 10.0 microns or larger.

Many important micron and submicron size particles can be separatedusing microporous membranes. For example, red blood cells are abouteight (8) microns in diameter, platelets are about two (2) microns indiameter and bacteria and yeast are about 0.5 microns or smaller indiameter. It is possible to remove bacteria from water by passing thewater through a microporous membrane having a pore size smaller than thebacteria. Similarly, a microporous membrane can remove invisiblesuspended particles from water used in the manufacture of integratedcircuits in the electronics industry. Microporous membranes arecharacterized by bubble point tests, which involve measuring thepressure to force either the first air bubble out of a fully wettedphase inversion membrane (the initial Bubble Point, or “IBP”), and thehigher pressure which forces air out of the majority of pores all overthe phase inversion membrane (foam-all-over-point or “FAOP”). Theprocedures for conducting initial bubble point and FAOP tests arediscussed in U.S. Pat. No. 4,645,602 issued Feb. 24, 1987, thedisclosure of which is herein incorporated by reference. The procedurefor the initial bubble point test and the more common Mean Flow Poretests are explained in detail, for example, in ASTM F316-70 and ANS/ASTMF316-70 (Reapproved 1976) which are incorporated herein by reference.The bubble point values for microporous phase inversion membranes aregenerally in the range of about two (2) to about one hundred (100) psig,depending on the pore size and the wetting fluid.

Methods and Systems for preparing the dope used to produce microporousmembrane are known in the art. There are numerous methods of preparingthe dope. Prior methods of dope preparation are discussed in backgroundsection of U.S. patent application Ser. No. 09/022,295, now U.S. Pat.No. 6,056,529 issued May 2, 2000, mentioned above under relatedapplications.

It is also known that processing relatively large bodies of dope, suchas that used in the production of microporous phase inversion membranes,is accompanied by many difficulties such as the need to formulateseparate dope batches for each size pore phase inversion membraneproduced as well as the problems in controlling the temperature of thedope during the batching process.

As was pointed out in the '295 application, during production runs ofmicroporous phase inversion membrane, it is important to producemicroporous phase inversion membrane having the desired pore size and/orpore size distribution.

As summarized in the '295 application, in the prior batch formulationprocess, the dope formulation (solvent, nonsolvent, polymer ratio) waskey to controlling pore size in the microporous phase inversionmembrane. Using the batch formulation method as a predictive control ofpore size in microporous phase inversion membrane, microporous phaseinversion membrane having a specific pore size was produced from aspecifically formulated dope batch.

As described in the '295 application, thermal manipulation to change thepore size in a membrane produced from a dope has long been recognizedand has been used in reprocessing out of specification dope, asdiscussed therein. However, this recognized property of the dope wasdependent on raising the temperature of the dope to a temperature higherthan that to which the dope had previously been processed. While oneprior patent mentioned in the '295 application discussed controlling theprocess temperature as one factor in enabling continuous production ofmaterial with fixed or variable pore size from a single batch of nylon46 solution, that prior patent failed to provide any specifictemperatures other than a wide temperature range. Further, in the onlyexample relative to varying pore size, the patent combined processtemperature manipulation with the composition of the dope and thecomposition of the bath to effectuate the pore size change but only inone direction, from smaller to larger. There was no apparent effort tocontrol the temperature of the solution at a specific temperature or anyeffort to try to lower the temperature of the solution to produce asmaller pore size.

Following the teachings of that particular prior patent, using thermalmanipulation to change the pore size and viscosity of the mixture, asthe solution is heated to higher temperatures, the viscosity of the dopebecomes such that it might not be usable in a solution castingoperation, unless controlled. Specifically, as the particular solutionis heated to higher temperatures, processing problems will most likelybe encountered including those related to viscosity, degassing ofvolatile components, foam formation and quenching problems, withoutadequate viscosity control.

The methods taught in that prior patent are not applicable to Marinacciostyle Nylon 66 dopes and the membrane products produced therefrom, forthe following reasons: 1) the patent is directed toward attempting toproduce a skinned membrane, with a radically altered pore structure justbelow the qualifying skin layer. In this method, the quality andintegrity of the skinned membrane is completely dependent on the qualityof the first few microns of surface thickness. With this method, eventhe smallest imperfection (air entrapment, substrate fiber breach, etc.)in the skin will destroy the integrity of the product. For this reason,the methods disclosed in the patent must restrict the casting solutionviscosity to a very narrow practical range, to ensure wetting of thesubstrate, minimization of entrapped air, and “smooth, even coating ofthe mixture,” to ensure the integrity of the finished membrane product.There is, however, a practical limit to the solution viscosity;therefore a single stage thermal treatment and hot casting wouldpotentially lower the viscosity to an impractical point, thus limitingthe useful range of resultant pore sizes. 2) Additionally, the singlestage thermal treatment and hot casting would be harmful to theresulting product, in that the volatile non-solvent components of theMarinaccio style dope (Methanol and Methyl Formate) will de-gas in anuncontrolled manner upon casting at a temperature above thirty-fourdegrees (34°) C. (boiling point of Methyl Formate), and form bubbles,voids and other imperfections in the surface and matrix of the membrane.These voids are not desirable in commercial microporous membrane.

In the end, the teaching of that prior patent appears ambiguous as tothe effect of temperature alone on pore size because smaller pore sizematerials could result primarily from 1) different casting dope solutionformulations, or 2) higher proportions of solvents in the bath as it wasknown that a range of different pore sizes could be produced from asingle solution by changing the proportions of solvents in the bath.

As summarized in the background of the '295 patent application, theprior art can be described as a non-real time predictive batch-typeprocess that uses formulation to initially control pore size and bulkreheating as a predictive thermal manipulation to produce a predictivepore size to correct an improperly formulated batch, or improperlycontrolled initial mix cycle, sheer speed control to introduce thenonsolvent in the preparation of the dope as a batch of liquid to beprocessed into a membrane and bath solvent control in order to vary thepore size. In some prior art, discussed above, at the end of theformulation process, the dope had a viscosity related to the processtemperature. There was no apparent attempt to independently control theviscosity of the dope prior to moving the dope to a membrane productionapparatus.

As with dope preparation, methods and systems for producing reinforcedmicroporous membrane are also known in the art. A number of priorpatents were discussed in the '979 and the '816 patent applications thathave been incorporated by reference. While there appears to have beenconsiderable effort to (1) develop methods and processes for preparingdopes which when processed into microporous membrane produce microporousmembrane having a specific pore size and (2) methods and apparatus formanufacturing reinforced microporous membrane, none of these effortsappear to have resulted in a system and method including the preparationof a mother dope connected to a reinforced microporous membranemanufacturing apparatus that is capable of producing reinforcedthree-zone microporous membrane having any one of a plurality ofdifferent dopes in any one of the three zones.

Thus, there is a need for systems and methods for continuouslymanufacturing a relatively thin, geometrically symmetrical, continuous,monolithic, reinforced, polymeric microfiltration membrane having atleast three independent and distinct pore size performance zones (onereinforced performance zone, presently preferably, central to themembrane structure, and two outer non-reinforced performance zonesincluding at least one outer qualifying performance zone on one side ofthe central reinforced zone and a second outer non-qualifying prefilterperformance zone on the other side of the central performance zone or,two outer qualifying performance zones, one on each side of the centralzone) progressing through the thickness of the membrane, each zone beingcontinuously joined throughout the membrane structure utilizing at leastone mother dope batch to provide any one of a plurality of differentpore size dope to any one of the three zones. Such systems and methodsshould produce a three-zone membrane structure by a highly robust,single unit operation, with on-line pore size and layer thicknessattribute control. Such systems and methods should produce a three-zonemembrane that meets the industry's long recognized need for superiorperformance and greater flexibility of triple layer composite structureshaving any one of a plurality of pore sizes in any one of the threezones. Such systems and methods for producing a three-zone membraneshould provide for the relatively inexpensive manufacture in acontinuous process with the capability of changing the pore size in anyof the zones including changing dope batches. Such systems and methodsof manufacturing a three-zone membrane should eliminate the complexproduction of traditional laminated single layer structure membrane andincrease the range of pore sizes and manageable handling thickness thatare provided by the non-reinforced zones. Such systems and methods formanufacturing a three-zone membrane should have a geometricallysymmetrical structure having improved utility, flexibility, andprocessability into finished industrial forms (pleated cartridges, etc.)while assuring structural integrity in any one of plurality of differentpore sizes in each of the three zones.

Such systems and methods of manufacturing a three-zone membrane shouldprovide a membrane having a minimum functional thickness and maximumthroughput at minimal pressure drops, high integrity and be economicallyproduced such that there is any one of plurality of different pore sizesin each of the three zones. Such systems and methods for manufacturing athree-zone microporous membrane should include the formulation of atleast one mother dope batch at a temperature equal to or below thetarget temperature for producing the smallest desired pore size of thepossible plurality of pore sizes for each zone to be produced from theat least one mother dope batch. Such systems and methods formanufacturing a three-zone microporous membrane should provide for theelevation of selected portions of the at least one mother dope batch toany one of a plurality of target temperatures such that microporousmembrane having any one of a plurality of corresponding pore sizes canbe simultaneously produced from at least one mother dope batch. Suchsystems and methods for the manufacture of a three-zone microporousmembrane should provide for the temperature control of at least aportion of the at least one mother dope batch to about ±0.2° C. of atarget temperature prior to that portion of the dope prepared at thetarget temperature and after cooling being transferred to at least onedope application apparatus of a reinforced, three-zone microporousmembrane manufacturing system at a processing site. Such systems andmethods for the manufacture of the three-zone microporous membraneshould provide for the accurate control of the temperature seen bysubstantially all of that portion of the dope to about ±0.15° C. priorto that portion of the dope being transferred to at least one dopeapplication apparatus of the reinforced, three-zone microporous membranemanufacturing system. Such systems and methods for manufacturingthree-zone microporous membranes should eliminate the necessity forpreparing at least one dope batch according to individual uniqueformulations for each pore size, thus resulting in significant costsavings and flexibility in the usage of dope batches. Such systems andmethods for manufacturing reinforced, three-zone microporous membranesshould also provide the ability to selectively change the pore size ofat least one zone of the three-zone microporous membrane being producedfrom the at least one mother batch after a certain amount of at leastone zone of the reinforced, three-zone microporous membrane has beenproduced at one specific pore size and begin producing reinforced,three-zone microporous membrane having another pore size in that samezone utilizing the same at least one mother dope batch.

SUMMARY OF THE INVENTION

An object of the present application is to provide systems and methodsfor manufacturing three-zone, reinforced, continuous, non-laminated,geometrically symmetrical microporous membrane possessing structuralintegrity.

Another object of the present application is to provide systems andmethods for manufacturing reinforced, three-zone continuous,non-laminated symmetrical microporous membrane exhibiting low pressuredrop and high flow rate across the membrane.

A further object of the present application is to provide systems andmethods for manufacturing reinforced, three-zone continuous,non-laminated, geometrically symmetrical microporous membrane which isparticularly suitable for the filtration of biological or parenteralfluids.

Yet a further object of the present application is to provide systemsand methods for manufacturing reinforced, three-zone continuous,non-laminated, geometrically symmetrical microporous membrane which isparticularly suitable for the filtration of high purity water for theelectronics industry.

Yet another object of the present application is to provide systems andmethods for manufacturing such a three-zone, continuous, reinforced,non-laminated, geometrically symmetrical microporous membrane.

In accordance with these and further objects, one aspect of the presentapplication includes a system for manufacturing three-zone microporousmembrane, the system comprising: at least one vessel for containing aternary phase inversion polymer mother dope; a dope processing site; atleast one pressure means, operatively connected to the at least onevessel, and the dope processing site for moving the dope from the atleast one vessel to the dope processing site; a dope transportationsystem, operatively connected to the at least one vessel and the dopeprocessing site, for transfer of the dope from the vessel to the dopeprocessing site; at least one thermal manipulation means, operativelyconnected to the at least one vessel and the dope processing site, fortransforming the dope into any one of a plurality of different possiblepore size producing dopes; and at least three dope application means,operative at the dope processing site and operatively connected to theat least one thermal manipulation means, for applying the dope at thedope processing site.

Another aspect of the present application includes a system formanufacturing three-zone microporous membrane, the system comprising: atleast one vessel for containing a ternary phase inversion polymer motherdope; a dope processing site, operatively connected to the at least onevessel containing the ternary phase inversion polymer mother dope; adope transportation system, operatively connected to the at least onevessel and to the dope processing site, for transporting the dope fromthe vessel to the dope processing site; pump means, operativelyconnected to the at least one vessel, for moving the dope from the atleast one vessel to the dope processing site; at least three thermalmanipulation means, operatively connected to the at least one vessel,the dope transportation system and the dope processing site, fortransforming the dope into any one of a plurality of different possiblepore size producing dopes; and at least three dope application means,each operatively connected to a respective one of the three thermalmanipulation means for application of the dope delivered to the dopeprocessing site.

Still another aspect of the present application includes a three-zonemicroporous membrane prepared by a method for manufacturing a three-zonemicroporous membrane, the method comprising the steps of: providing atleast one vessel for containing a ternary phase inversion polymer motherdope; formulating a ternary phase inversion polymer mother dope in theat least one vessel to effect dissolution and equilibrium mixing of thepolymer, solvent and nonsolvent; maintaining the mother dope in thevessel at a temperature sufficient to stabilize and maintain the dopeformulated after cooling from the formulation temperature; providing adope processing site having at least three dope application means;operatively connecting the at least one vessel to the dope processingsite such that the mother dope is transported from the at least onevessel to the dope processing site; operatively positioning at least onethermal manipulation means between the at least one vessel and the dopeprocessing site; thermally manipulating the mother dope transported fromthe at least one vessel in the at least one thermal manipulation meansinto any one of a plurality of different possible pore size producingdopes; and applying a predetermined one of the plurality of differentpossible pore size producing dopes received from the at least onethermal manipulation means to a scrim at the dope processing site toproduce reinforced, three-zone microporous membrane.

Other objects and advantages of the invention will be apparent from thefollowing description, the accompanying drawings and the appendedclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of the systems of the presentapplication;

FIG. 2 is a schematic representation of one Dial-A-Por™ apparatusmodified to supply dope to two separate dope application mechanism ormeans at the dope processing site;

FIG. 3 is a schematic of one representative Dial-A-Por™ apparatus thatcould be incorporated into the system of FIGS. 1, and 8-10 for carryingout the methods of present application;

FIG. 4 is a plan view of a representative configuration for the thermalmanipulation mechanism or means, including the pump, the heatingmechanism or means and the cooling mechanism or means previously used asa stand alone unit portions of which are useful with the systems of thepresent application for carrying out the methods of the presentapplication;

FIG. 5 is a schematic representation of a specific dope processing siteuseful with the systems and methods of the present application;

FIG. 6 is a detailed, enlarged perspective view of a scrim positionedbetween the opposed dies of FIG. 5, with a portion of one die partiallybroken away;

FIG. 7 is a cross-section schematic of a representative reinforced,three-zone, microporous membrane produced by the systems and methods ofthe present application;

FIG. 8 is a schematic representation of an alternative system of thepresent application;

FIG. 9 is a schematic representation of another alternative system ofthe present application;

FIG. 10 is a schematic representation of still another alternativesystem of the present application;

FIG. 11 is a schematic representation of an alternative Dial-A-Por™apparatus modified to supply dope to two separate dope applicationmechanisms or means at the dope processing site;

FIGS. 12a-b are scanning electron photo micrographs of a reinforcedthree-zone microporous membrane manufactured by the systems and methodsof the present application illustrating the inter-face of the threeporous zones at 500× and 2,500×;

FIGS. 13a-b are scanning electron photo micrographs of a reinforcedthree-zone microporous membrane manufactured by the systems and methodsof the present application illustrating the interface of the threeporous zones at 500× and 2,500×; and

FIGS. 14a-b are scanning electron photo micrographs of a reinforcedthree-zone microporous membrane manufactured by the systems and methodsof the present application illustrating the inter-face of the threeporous zones at 500× and 2,500×.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Microporous phase inversion membranes produced using the systems andmethods of the present application are preferably produced from nylon.The term “nylon” is intended to embrace film forming polyamide resinsincluding copolymers and terpolymers which include the recurring aminogrouping and blends of different polyamide resins. Preferably, the nylonis a hydrolytically stable nylon possessing at least about 0.9 moles ofamino end groups per mole of nylon as described in U.S. Pat. No.5,458,782, the disclosure of which is incorporated herein by reference.

While in general the various nylon or polyamide resins are allcopolymers of a diamine and a dicarboxylic acid, or homopolymers of alactam and an amino acid, they vary widely in crystallinity or solidstructure, melting point, and other physical properties. Preferrednylons for use with the methods and systems of this application arecopolymers of hexamethylene diamine and adipic acid (nylon 66),copolymers of hexmethylene diamine and sebacic acid (nylon 610),homopolymers of polycaprolactam (nylon 6) and copolymers oftetramethylenediamine and adipic acid (nylon 46). These preferredpolyamide resins have a ratio of methylene (CH₂) to amide (NHCO) groupswithin the range of about 4:1 to about 8:1, most preferably about 5:1 toabout 7:1. The nylon polymers are available in a wide variety of grades,which vary appreciably with respect to molecular weight, within therange from about 15,000 to about 42,000 (number average molecularweight) and in other characteristics.

The highly preferred species of the units composing the polymer chain ispolyhexamethylene adipamide, i.e. nylon 66, having molecular weightsabove about 30,000. Polymers free of additives are generally preferred,but the addition of antioxidants, surface active agents, chargemodifying agents or similar additives may have benefit under someconditions.

As mentioned in the background of the '295 application, one conventionalmethod for processing dope containing the above mentioned polamideresins into microporous phase inversion membrane is carried out byformulating a specific dope according to a known formula to produce acertain pore size when the dope is cast into microporous phase inversionmembrane. The dope comprises a polymer, a solvent and non-solvent in aspecific predetermined amount mixed and stored in a sealed storagevessel. Once the dope batch is formulated in accordance with apredetermined formula under controlled conditions including a maximummixing temperature, the dope is then pumped to a casting line and atthat point cast into a microporous phase inversion membrane.

As was indicated in the background of this art in the '295 application,one of the problems discovered was the inconsistency of pore sizesobtained from conventionally formulated dope batches supposedlyidentically formulated and controlled to a specific maximum temperatureand mix history during formulation. However, when some of these out ofspecification dope batches were reprocessed at a supposedly highertarget temperature, there was no noticeable change in the pore size ofthe phase inversion membrane produced therefrom. Thus, it became evidentthat once the dope was heated to a certain temperature, the pore sizeformed in microporous phase inversion membrane produced from that dopecould not be changed to a smaller pore size when the dope wasreprocessed by reheating to a temperature lower than the temperature towhich the dope had already been elevated. In other words, when thisphenomenon occurred, the temperature to which the dope had been exposedto during formulation was in fact higher than that to which it wasbelieved the dope had been exposed. This indicated that exacting processcontrol of dope temperature during formulation was important in order toachieve the target specification pore size for the microporous phaseinversion membrane.

It was determined in the '295 application that once a dope has beenprocessed at a certain temperature, and that temperature is atemperature higher than the temperature necessary to produce aparticular pore size, then the dope retains the memory of having beenprocessed at the higher temperature. Thus, even though the dope had beencooled to room temperature, reheating the dope to a temperature lowerthan that temperature previously attained during formulation orreheating, any microporous phase inversion membranes produced therefromwould have pores corresponding to the pore size of the highesttemperature at which the dope had previously been processed. Thesmallest possible pore size was a direct result of the thermal historyof the specific dope batch. Thus, thermal heat treatment of dope onlyworks in one direction and that is to enlarge the pore size of theresultant membrane, not to decrease pore size of the resultant membrane.Specifically, it has now been determined that there is a “temperaturememory” associated with the polymer mixture and that the pore size inany membrane produced therefrom is associated with the highesttemperature to which the polymer mixture has been exposed prior to beingprocessed into membrane. This “temperature memory” is permanent as faras a specific temperature is concerned. Thus, once the dope has beenexposed to a certain temperature, the dope can never exhibit theproperties associated with dope exposed to a temperature below thehighest temperature to which it has been exposed but can exhibit theproperties associated with dope exposed to a higher temperature if it isexposed to a higher temperature.

The systems and methods disclosed in that Ser. No. 09/022,295application, U.S. Pat. No. 6,056,529, modified the prior methods andsystems described in the background of that application to takeadvantage of this thermal memory by, presently preferably, formulatingat least a single mother dope batch, under tightly controlledconditions, in a vessel at a low temperature, typically about twenty-onedegrees (21°) C. to about thirty-four (34°) C. and, presentlypreferably, at the maximum non-solvent to solvent ratio possible, at thespecific formulation weight percentage of the polymer, it beingunderstood that the mother dope batch is formulated at a temperaturebelow the temperature normally associated with the formation of thesmallest desired pore size to be produced in a reinforced, three-zonemicroporous membrane from that particular mother dope batch formulation.

As described in that application, only a relatively small portion of themother dope batch contained within the vessel was transported via apump, preferably a metering pump, from the vessel to a, presentlypreferably, thermal manipulation mechanism or means including a firstheating zone for elevating the temperature of that relatively smallportion of the dope. Then, the smaller portion of the dope was pumped toa second heating zone of the thermal manipulation mechanism or means,for incrementally elevating the temperature of the dope to a targettemperature. The thermally manipulated dope was then transported to acooling zone where the dope was cooled to a temperature and a viscositysufficient for processing at the dope processing site into at least onezone of a reinforced, three-zone microporous phase inversion membrane,it being understood that the viscosity of the cooled dope, alreadythermally manipulated to produce a specific pore size, may beindependently manipulated by controlling the cooling temperature inorder to optimize the viscosity of the dope at the reinforced,three-zone membrane manufacturing apparatus.

The, presently preferred, mother dope for producing the widest range ofpossible pore sizes from the smallest to the largest pore size wasformulated to provide a dope with the maximum non-solvent to solventratio attainable at the specific formulation weight percentage of thepolymer. It was understood that the ratio of non-solvent to solventcould be less than the maximum and still produce a range of pore sizesbut not necessarily provide the maximum flexibility to produce phaseinversion membrane having the widest possible range of pore sizes.

Once the relatively small portion of the mother dope batch had beenpumped from the vessel to a first thermal manipulation mechanism ormeans heating zone, the temperature of the small portion of the dope inthe first heating zone was, presently preferably, elevated to withinabout two degrees (2°) C. below a predetermined target temperature. Thepredetermined target temperature can be any of a plurality of possibletarget temperatures at which the dope has been determined to yield aparticular microporous phase inversion membrane pore size when processedinto microporous phase inversion membrane. The temperature of the dopewithin that first heating zone was then elevated to within about ±0.5°C. of about 2° C. below the target temperature by using temperaturecontrol apparatus, as will be explained below. Thus, the highesttemperature that the small portion of the dope was exposed to during themovement of the dope through the first heating zone of the first thermalmanipulation mechanism or means was, presently preferably, about 1.5° C.below each specific predetermined target temperature.

After achieving the desired temperature of about 2° C. below thespecific target temperature in the first heating zone, the relativelysmall amount of dope was further processed through the second heatingzone wherein the temperature of the dope was further elevated andcontrolled to within about ±0.15° C. of the one specific targettemperature. Upon achieving a dope temperature of about ±0.15° C. of onespecific target temperature, the dope exited the second heating zone ofthe thermal manipulation mechanism or means and was, presentlypreferably, cooled in a cooling zone of the thermal manipulationmechanism or means to a temperature, presently preferably, abouttwenty-one degrees (21°) C., or other temperature that provides the dopewith an appropriate viscosity for appropriate application and, aftersampling and testing, was further pumped to a microporous phaseinversion membrane production facility or dope processing site forprocessing into microporous phase inversion membrane having thepredetermined pore size corresponding to the target temperature.

It is an important advantage of the systems and methods of the presentapplication that the dope be thermally manipulated to a precisepredetermined temperature that produces a specific pore size inmicroporous phase inversion membrane and was then cooled back down to atemperature which independently controls the viscosity of the dopeduring the casting process, all within about ten (10) minutes,considerably less time than any known process has previously controlledthe temperature elevation phase alone during, such as, reprocessing anout of specification dope.

As described in the prior application, after exiting the dope coolingzone, a valve located in the dope process line provides for thewithdrawal of dope samples from the line for testing to ensure that thedope will produce microporous phase inversion membrane having thespecific pore size desired. Additionally, the valve also provides forthe recirculation of the dope after the dope exits the cooling zone andreturns the dope to the dope process line at a point prior to the firstheating zone or other location, as appropriate.

Another important advantage of thermally manipulating dope includes thesurprising ability to produce, from a single mother dope, phaseinversion membrane having a range of pore sizes greater than previouslyproduced, from about 0.05 microns or smaller to about 50 microns orlarger, an order of magnitude of about three (3). By using this method,microporous membrane production can be accomplished in any sequence aslong as the desired pore size is not one that requires an initialformulation mixing temperature less than the formulation mixingtemperature of the mother dope.

The methods and systems of the above described systems and methods forthermally manipulating the pore size in dopes use real time essentiallyinstantaneous, about ten (10) minutes or less and no more than aboutfive (5) to about (20) twenty minutes for the total thermal manipulationcycle as opposed to three to five hours for the prior art thermalmanipulation to independently control dope viscosity and resulting phaseinversion membrane pore size in the production of phase inversionmembrane. The systems and the methods of the present application aredesigned to exploit, to the maximum advantage, the permanent thermalmemory of the phase inversion membrane casting dopes.

As described in the prior application, thermal manipulations occurbetween the inlet to the first heat exchanger and the outlet of thefinal cooling mechanism or means or heat exchanger. When the '295application was filed, volume of about five gallons of the dope wasbeing processed through the thermal manipulation mechanism or means(heat exchangers) at any one time between those two points at a speed ofabout one-half (0.5) to about three-quarters (0.75) of a gallon perminute (GPM). At a process speed of about one half gallon per minute,the about five (5) gallons of dope are thermally manipulated in aboutten (10) minutes or less to a point where the dope was ready for coatingat a coating apparatus. When providing dope from a single mother dopevessel through only one thermal manipulation mechanism or means (seeFIG. 3) and with the particular apparatus used at that time, theseamounts and rates were found to be appropriate. However, when using twoor three thermal manipulation mechanisms or means to provide dope from asingle mother dope vessel to two or three coating mechanisms, about 2gallons of the dope is now being processed through each thermalmanipulation mechanism at any one time between the inlet to the thermalmanipulation mechanism and the outlet of the final cooling mechanism ata speed of about 0.3 for about 0.9 gallons per minute per eachDial-A-Por™ unit branch for a total of about 1.0 gallon per minute whenall three Dial-A-Por™ unit are in operation (see FIG. 1). At the processspeed of about one gallon per minute, then about 2 gallons of dope ineach Dial-A-Por™ unit is thermally manipulated in about ten (10) minutesor less to the point where the dope is ready for coating at the coatingapparatus.

The temperature manipulation of the systems and methods of the presentapplication is accomplished by precisely controlling the temperature ofthe dope as the dope is pumped through each of the heat exchangers to avery precise point over a large surface area or heat transfer areawithin the first and third heat exchangers so that essentially eachelement of the fluid sees essentially the same temperature manipulation.In the second heat exchanger, the static mixer/heat exchangercontinuously pushes fluid, such as dope, from the center of the heatexchanger to the wall than back to the center again, substantiallyeliminating thermal gradients and boosting the inside film coefficientto essentially convert laminar flow to turbulent flow to enhance mixing.

An illustrative system utilized for preparing, moving or pumping andcontrolling the temperature of a mother dope batch to a predeterminedtarget temperature to produce at least one predetermined pore size in areinforced three-zone microporous phase inversion membrane in accordancewith the system and methods are described below. Referring nowparticularly to the accompanying drawings, FIG. 1 is a schematicrepresentation of one representative system 10 for implementing themethods of the present application. As shown, the system 10 includes aplurality of processing stations and processing mechanisms beginningwith the mother batch of dope contained in the storage vessel 12,presently preferably, under about forty-five (45) psi pressure, andending with the dope being processed at a dope processing site 14 intoreinforced, three-zone microporous phase inversion membrane 101 (seeFIG. 7).

The systems and methods of the present application begin with thepreparation of a mother dope, as described in the Ser. No. 09/022,295application, U.S. Pat. No. 6,056,529. The dope is then transported to atleast one thermal manipulation mechanism or means, or Dial-A-Por™ unitand preferably at least two Dial-A-Por™ units where the dope isincrementally thermally manipulated to provide a dope that, whendelivered to and coated on a scrim through dope application mechanism ormeans at the dope processing site, as described in the Ser. No.09/040,979 and the Ser. No. 09/040,816 applications, now U.S. Pat. Nos.6,264,044 and 6,056,529, yields a specific pore size in the appropriatezone of a reinforced, three-zone microporous membrane. While the onlyone Dial-A-Por™ unit is described in detail below, it is understood theother two Dial-A-Por™ units depicted in FIG. 1 are similarlyconstructed.

As mentioned above, the membrane production process begins byformulating a mother batch of dope by mixing various constituents knownin the art in a conventional dope storage vessel 12. Dope preparation issimilar to the dope preparation discussed in U.S. Pat. No. 4,645,602,issued on Feb. 24, 1987, assigned to the assignee of the presentapplication, the disclosure of which is incorporated herein byreference. The sealed storage vessel 12 is typically maintained in aninert nitrogen atmosphere from about zero (0) to about fifty (50) psig.Presently, the vessel is preferably pressurized to approximatelyforty-five (45) psig with nitrogen.

The storage vessel 12 includes conventional temperature controlmechanism or means, such as, for example, a water or liquid jacketsurrounding the dope and conventional fluid mixing mechanism or means 16such as a rotating device for agitating the dope inside the storagevessel 12 (see FIG. 3). Fluid transport mechanism or means 18 such as,for example, conventional pipe or hose, are operatively connected to thebottom 20 of the vessel 12 for sequentially transporting a small portionof the dope, after stabilizing the formulation, initially at atemperature of about twenty-one degrees (21°) C. to about twenty-eight(28°) C. (or any suitable initial processing temperature for the dope)contained in the vessel to a coating apparatus.

As illustrated in FIG. 3, a, presently preferably, 150 micron filter 22for separating foreign matter, solid contaminants and any suspendedparticulate solid particles from the dope is operatively positioned inthe hose. One filter 22 found to be useful in performing this functionis, presently preferably, a CTG-KLEAN filter housing manufactured byCUNO as Part No. 1WTSR1 with a 150 micron cartridge installed.

As illustrated in FIG. 5, the scrim 102 is fed by the conventional drivesection, downwardly between, presently preferably, a series of dies,including the first die 126 for, presently preferably, completelypressure impregnating the scrim 102 with a first dope 108 and second 128and third 130 dies for coating a second 110 and a third 116 dope on tothe outer surfaces 112, 118 of the dope impregnated scrim 114. In oneapparatus useful to produce reinforced, three-zone microporous membrane,the first die 126 is a single slot die, operatively connected to asuitable reservoir 60 containing the first dope 108 or, presentlypreferably metering pump 402 (see FIG. 8) for delivering the first dope108 to the die 126 at the appropriate pressure. The first dope may varydepending on the type of film-forming polymer used, but is generally aliquid dope formulated and treated to produce a specific pore size whenquenched. A conventional controlled pumping mechanism or metering pump402 (schematically shown) operates to selectively deliver the first dope108 from the reservoir 60 or from the Dial-A-Por™ unit 25 to the firstdie 126. The first die 126 has an opening configured to provide an evenamount of the first dope 108 so as to pressure impregnate the scrim 102as the scrim 102 passes by the opening of the first die 126. Whendifferent sizes of scrim 102 are used, the die 126 may be changed forappropriate scrim impregnation. It is important that the first dope 108transferred to the scrim 102 substantially completely saturate orimpregnate the scrim, as was discussed above.

After the scrim 102 is at least substantially impregnated or saturatedwith the first dope, the scrim travels between the second 126 and third130 dies. In one embodiment of the apparatus, the scrim 102 is disposedvertically and travels in the downward direction. In one, presentlypreferred embodiment of the apparatus, the scrim 102 may initiallytravel at an angle less than vertical, as illustrated in FIG. 2. Second126 and third 130 dies are essentially disposed on opposite sides of thescrim 102 in order to produce the membrane of the present invention.Second die 128 is directed to coat the polymer dope 110 desired onto thefirst surface 112 of the substantially saturated scrim 102 and in likemanner, third die 130 is directed to coat the polymer dope 116 desiredonto the second surface 118 of the substantially saturated scrim 102.Each die 128, 130, is fed from a reservoirs 62, 64 having the dopes 110,116 or from a metering pump 400, 404, as illustrated in FIG. 8. It is tobe appreciated that the dopes may be a combination of any of thewell-known film-forming polymers in an appropriate well-known solvent.Controlled pumping mechanisms or metering pumps 400, 404 selectivelydeliver the dope 110, 116 to the dies 128, 130.

As best shown in FIGS. 5 and 7, the dies 128, 130 are each disposed onopposite sides of the pressure impregnated scrim 102 and essentiallyopposed to the other die. Each die 128, 130 has a chamber 272 forreceiving the dope solution and a narrow slot 274, transverselyextending across each side of the front 275 of each die, for firsttransferring the dope solution onto the impregnated scrim 102 (via die126) and then to coat the substantially saturated scrim on both sides112, 118 (via dies 128, 130). The dope is forced out of the slots 274 ineach die by the pressure supplied by the metering pumps (not shown), ina manner known in the art.

The pressure provided to the dope varies with each dope and scrim used.Determination of the appropriate pressure for any of the dopes appliedto a particular scrim can be determined by those skilled in the art. Thedies 128, 130 are positioned close enough to the substantiallysaturated, impregnated scrim 102 so that the dope directly contacts theouter surface of the dope saturated scrim 102 when the dope is forcedfrom the slot 274. As is apparent in FIG. 6, the length of the slot 274determines the final width of the dope coated onto the saturated scrim.By masking or other appropriate means, it is possible to foreclosecoating the dope at the edges of scrim 102, leaving a selvage area 276for trimming, potting or other post-formation operations.

It is to be understood that the initial dope may be different from theother dope(s) and that it is possible to have three different dopes,with a first dope impregnating the scrim 102 and the second and thirddopes coated on each side of the first dope impregnated scrim, resultingin a graded density three-zone membrane.

In one specific embodiment, further downstream from the vessel 12 is ametering pump 24, similar to that of FIGS. 3 and 9, for incrementallytransporting a relatively small portion of the dope contained in thevessel 12 from the vessel to the dope processing site 14. One pump foundto be useful for this function is a type 1 rotating gear pumpmanufactured by Roper Pumps, model number 005SSIPT4DJMCW, deliveringabout 0.03 to about 0.5 gallon per minute.

As illustrated in FIG. 3, downstream from the pump 24 and operativelyconnected thereto is a first thermal manipulation means or Dial-A-Por™unit 25 (See FIG. 1) which includes a first mechanism or means or firstheating means 26, for elevating or increasing the temperature of thesmall portion of the dope to within, presently preferably, about twodegrees (2.0°) C. below a predetermined temperature. As illustrated inFIGS. 3 and 4, the first heating means 26 includes a temperaturecontroller 28, (shown schematically in FIG. 3). One specific modeltemperature controller found useful for this function is a Conair WaterTemperature Controller having about a ±0.2° C. accuracy using anexternal resistant temperature devise (RTD) probe (Thermalator TemptracSeries, model number TTP1-D1 with direct injection utilizing a motorizedmodulator valve and an Aethena Series XT16 and dual output controller).The temperature controller 28 is operatively connected to a plate heatexchanger 30, presently preferably, having about a twenty (20) squarefoot heat transfer area or any area sufficient to accomplish thetemperature elevation of the dope to about two degrees (2.0°) C. below apredetermined target temperature. Such a plate heat exchanger 30 isavailable from Tranter, as Model No. MX-20-0412-UP-080/0.060.Preferably, the controller 28 is configured to measure the process fluid(water) in the opposite direction of dope flow (counter current).

As illustrated in FIG. 3, after exiting the first heating means 26 thedope is, presently preferably, transferred to a second mechanism ormeans or second heating means 32 for further increasing or elevating thetemperature of the dope. The second means 32, presently preferably,consists of a jacketed pilot mixer/heat exchanger 34 such as, forexample, those available from Chemineer as a Kenics HX-1/2 Jacketedpilot mixer/heat exchanger, Part No. 033-00128. The temperature of themixer/heat exchanger 34 is, presently preferably, controlled by a heatedcirculating water bath programmable controller 36 having a temperaturecontrol capability of about ±0.01° C. with a display having an accuracyof only about ±0.2° C. One programmable controller found useful toperform this function was a Haake (USA) model number N8-B7, 3KW heatingcirculator, with the dope temperature being controlled by an externalresistance temperature device (RTD/PT100) 70. Preferably, the controller36 is configured to measure the process fluid (water) in the oppositedirection of dope flow (counter current).

After the dope has been processed through the second heating means 32and after the dope temperature has been elevated to about ±0.15° C. ofthe target temperature, the dope is then cooled in a cooling mechanismor means 40. The cooling means 40 includes a heat exchanger 41 and acontroller 45. The cooling means 40, is used to reduce the temperatureof the relatively small amount of dope exiting the second heating means32 at the target temperature to the ambient coating temperature of abouttwenty one degrees (21°) C., or other temperature which provides anappropriate dope viscosity, while the dope is being processed through aheat exchanger 41 having about a 20 sq. ft. heat transfer area. One heatexchanger found to be acceptable to perform the heat exchanger functionis a Tranter, Model No. MX-20-0412-UP-080/0.060 heat exchanger.Apparatus found useful to perform the control function is a Thermal CareAccuchiller Model NO. AQOAO3 air cooled portable chiller having atemperature control accuracy of about ±1° C. Preferably, the controller45 is configured to measure the process fluid (water) in the oppositedirection of dope flow (counter current).

After the dope is cooled in the cooling means 40, the dope is pumped toa valve 42 (in FIG. 3) operatively positioned in the dope process loop46 where samples of the dope exiting the cooling means 40 to can bedrawn and tests can be run thereon to determine the pore size that thedope will produce in microporous membrane after coating. Anotherposition 44 for the valve 42 provides for dope recirculation within thedope process line to a position between the storage vessel 12 and themetering pump 24 or other appropriate location.

When the valve 42 is in the recirculation position 44, a recirculationloop 46 can be actuated, which enables the system to reach a steadystate temperature prior to the membrane coating being commenced at thedope processing site 14. Additionally, running in the recirculation loop46 prevents the production of out-of-specification microporous phaseinversion membrane until after receiving the test results from thesamples taken of the dope exiting the cooling means 40. Once it isdetermined that the dope has, in fact, been stabilized at theappropriate predetermined target temperature for producing theappropriate pore size in microporous membrane, then the valve 42 can bemoved to position 50 to deliver the dope to the dope processing site 14.

Additional components of the dope processing system 310 include pressuregauges 60 positioned at various locations as illustrated in FIG. 3. Thepressure gauges positioned on either side of the pump 24 obtain thedifferential pressure across the pump and the head pressure to the pump.Additional pressure gauges are operatively positioned downstream fromeach heat exchanger means, 26, 32, and 40 to monitor the pressure dropafter the dope has processed through each heat exchanger means forundesirable pressure build up.

Omega thermistors 62 having a precision of about ±0.15° C. areoperatively positioned on the downstream sides of the first 26 and thesecond 32 heat exchanger means for providing a more accurate temperaturereading of the downstream process than the Conair or the Haake unitsdisplays are capable of providing. The thermistors 62 provide thecapability to read the temperature to an accuracy of about ±0.15° C. forincreased temperature control whereas the Haake unit is capable ofcontrolling the temperature accuracy to ±0.01° C. One additional featurein the system of the present application includes a pressure reliefvalve 64 operatively positioned in the loop 46 for protecting the systemfrom damage from excess pressure buildup by taking the pump out ofoperation should the pressure exceed a predetermined pressure, presentlyabout 250 psi. If the pressure were to exceed a certain pressure, thenthe dope would be recirculated through the pump via hose 66 (see FIG.4).

An RTD 70 is operatively positioned in the loop and connected to theHaake recirculation bath 36 for controlling the temperature of the dopein the second heat exchanger means 32. Another RTD probe (not shown) islocated inside the Haake recirculation bath 36. In operation, theexternal RTD probe 70 is the controlling loop unless the probe indicatesthat the temperature of the dope is outside the maximum setpointdifferential, control reverts to the internal RTD probe for controllingthe process to the setpoint. The Haake is a proportional band controllerutilizing Fuzzy Logic PID having the two above described RTDs, oneinternal and one external to minimize the temperature differentialbetween the dope and the process fluid.

It is now possible to combine the first 26 and second 32 heating meansof each Dial-A-Por™ into a single heating means, so that the resultingtemperature coming out of the single heating means could be controlledto within at least about ±0.2° C. of the target temperature. Thepreviously described Conair unit is capable of such control.

The Dial-A-Por™ units 25, 140, 142 are, in their presently preferredembodiment, two stage units which use the high temperature memory of adope to control pore size, and the cooling cycle to independentlycontrol the viscosity of the dope at a coating apparatus. In thismanner, the thermal manipulation of the dope alone is sufficient toproduce a wide range of commercially useful phase inversion membranesfrom a single starting dope.

As schematically illustrated in FIG. 5, one, presently preferred, dopeprocessing site 14 or vertical casting line (VCL) apparatus 100 andmethod for manufacturing a reinforced, three-zone continuous,geometrically symmetrical microporous filtration membrane 101 (see FIG.7) includes: providing a porous support material 102 having first 104and second 106 sides, presently preferably, pressure impregnating thesupport material 102 with a first solution or dope 108 processed to afirst temperature, coating a second solution or dope 110 processed to asecond temperature over the first side 112 of the pressure impregnatedsupport material 114, coating a third solution or dope 116 processed tothe second temperature or to a third temperature over the second side118 of the pressure impregnated support material 114 such that acontinuous microporous membrane having a middle zone 120 disposedbetween an upper zone 122 and a lower zone 124 (See FIG. 7) formed fromthe first 108, second 110 and third 116 dopes, the support material 102being, presently preferably, completely embedded within the middle zone120 and the middle zone having a pore size at least about twenty percent(20%) greater than the pore size of at least one of the upper zone 122and the lower zone 124.

The novel arrangement of slot dies 126, 128, 130 to, presentlypreferably, first pressure impregnate the support material 102 with afirst dope 108 and then to coat both sides thereof with other dopes hasbeen found particularly effective to produce the membrane 101. Asspecifically shown in FIG. 5, one of the presently preferred apparatus100 for manufacturing the membrane 101 at the dope processing site 14,in accordance with the systems and methods of the present application,includes a first die 126 for pressure impregnating the support materialor scrim 102 and substantially opposed second and third dies 128, 130for substantially simultaneously coating both sides 112, 118 of theinitially impregnated scrim 102 or other apparatus capable of coatingthe impregnated scrim as described above.

The three-zone microporous membrane 101 produced by the system andmethods of the present application is generally produced by firstpressure impregnating the scrim with a first dope and then coating anyone of a plurality of possible different dopes containing a film-formingpolymer in a solvent system onto each side of the dope impregnated scrimand immediately quenching the dopes 108, 110, 116 in a bath 138comprised of a conventional nonsolvent system for the polymer. It ispresently believed that an important parameter responsible fordevelopment of micropores in the membrane (e.g. pore size) is thesolvent system employed with the polymer and the nonsolvent system usedin quenching the polymer film as well as the phenomena discussed in thepreviously mentioned patent application. The selection of the solventfor the polymer is determined by the nature of the polymer material usedand can be empirically determined on the basis of solubility parameters,as is well known and conventional in the art.

As illustrated in FIG. 1, one, presently preferred, system 10 formanufacturing reinforced, three-zone microporous membrane includes atleast one vessel 12, presently preferably, containing a mother dopeoperatively connected to at least three Dial-A-Por™ dope thermalmanipulation units 25, 140, 142 with each of the Dial-A-Por™ units beingconnected respectively to the first 126, second 128 and third 130 slotdies. As illustrated, the system 10, presently preferably, includes asingle mother dope vessel 12 from which the dope can be pumped or movedby pressure on the dope in the vessel to a dope transporting mechanismor means piping system 144 having at least three branches 146, 148, 150,each branch being operatively connected to each of the three slot dies,respectively or be pumped, as illustrated in FIG. 3. Operativelypositioned between each of the dies and the mother dope vessel are thethree separate Dial-A-Por™ units 25, 140, 142. Each Dial-A-Por™ unit iscapable of thermally manipulating a portion of the dope from the motherdope batch to a specific predetermined temperature which produces apredetermined pore size and then delivering that thermally manipulateddope to the slot die operatively connected thereto, as described above.

Alternatively, additional dope containing vessels 152, 154 can also beoperatively directly connected to each of the three Dial-A-Por™ units.Each of these vessels may contain a specific mother dope as describedearlier in the application or it may contain a specific dope formulatedto produce a specific pore size or a dope made of a different polymer.

Specifically, as illustrated in FIG. 1, one dope containing vessel 12 isoperatively connected to the dope transporting system and to the firstDial-A-Por™ unit 25, a second dope containing vessel 152 is operativelydirectly connected to the dope transporting branch system 148 and to thesecond Dial-A-Por™ unit 140 and a third dope containing vessel is 154 isoperatively directly connected to the dope transporting system branch150 and to the third Dial-A-Por™ unit 142. Liquid flow controlmechanisms or means or valves 160, 161, 162 are operatively positionedbetween the dope transporting system 144 and the first dope containingvessel 12, the second dope containing vessel 152 and the third dopecontaining vessel 154, respectively, so that the flow of dope from eachdope containing vessels, 12, 152 , 154 to each of the Dial-A-Por™ unit25, 140, 142 from the respective vessels 12, 152, 154 can be selectivelycontrolled.

One of the dope containing vessels 12 is, presently preferably,connected directly to the dope transporting system 144 via valve 161 forthe first Dial-A-Por™ unit 25 and this particular dope transportingsystem 146 is also interconnected by pipes, 166, 168 to both of theother two Dial-A-Por™ transporting system branches 148, 150. Valves 170,172 are operatively positioned in the interconnected dope transportingsystem branches 166, 168 so as to selectively control the flow of dopefrom the center mother dope vessel 12 to either of the secondDial-A-Por™ 140 or third Dial-A-Por™ 142 units. Further, dope bypassmechanisms or means 180, 182, 184 including, such as, for example, pipes186, 188, 190 and valves 192, 194, 196, 198, 200, 202 are operativelyconnected to the dope transportation system branches 146, 148, 150before and after each Dial-A-Por™ unit 25, 140, 142 so that the dopeflowing therein can be diverted around each Dial-A-Por™ unit to flowdirectly to a selected slot die 126, 128, 140 without being processedthrough any one of the Dial-A-Por™ units. The valves 192, 194, 196, 198,200, 182 are, presently preferred, positioned in the intersection of thedope transportation means 146, 148, 150 and the dope bypass means, 180,182, 184 before and after each Dial-A-Por™ unit 25, 140, 142 operativelypositioned in the dope transporting means 144.

In one preferred system and method, a single dope vessel 12 isoperatively connected to the three Dial-A-Por™ units 25, 140, 142. Inoperation, the dope vessel 12 is filled with a mother dope as describedabove, and the dope is then simultaneously moved by a pump integral witheach Dial-A-Por™, as illustrated in FIG. 3, or pressure on the dopecontained in the vessel 12 through the dope transporting mechanism ormeans 144 to the first Dial-A-Por™ 25, the second Dial-A-Por™ 140 andthe third Dial-A-Por™ 144 unit, respectively. In each of the Dial-A-Por™units 25, 140, 142, the dope is selectively thermally manipulated to apredetermined temperature corresponding to a desired pore size and isthen transported to the respective predetermined slot die according tothe predetermined pore size desired to be produced in a reinforced,three-zone microporous membrane after being applied/coated by therespective slot die 126, 128, 130. Each Dial-A-Por™ unit 25, 140, 142may thermally manipulate the dope processed therethrough to threedifferent temperatures producing three different pore sizes.Additionally, two of the three Dial-A-Por™ units may thermallymanipulate the dope to the same temperature to produce the same poresize in two of the zones of the three-zone membrane.

Alternatively, any combination of one, two or three dope vessels 12,152, 154 could be utilized to provide a mother dope from each vessel toeach respective Dial-A-Por™ units where each respective dope wouldundergo thermal manipulation to produce a dope that would provide aspecific predetermined pore size to each of the respective slot dies.

In another system and method, at least one, and as many as all three ofthe dope vessels could contain dope formulated to produce a specificpore size, such dope being transported to the respective slot die, butbypassing each of the respective Dial-A-Por™ units.

In still another preferred system and method, any two of the Dial-A-Por™units could be bypassed by receiving dope directly from vesselscontaining dope formulated to produce a specific pore size for deliveryto two of the slot dies, with the third slot die receiving dope from avessel containing a mother dope, processed through one of theDial-A-Por™ units to deliver dope for providing any one of the pluralityof predetermined pore sizes at the third slot die.

In still another preferred system and method of the present application,pore size specific preformulated dope could be delivered to one slot dieby bypassing the Dial-A-Por™ unit, and dope from a single mother batchdope in one vessel could be processed through the other two Dial-A-Por™units to deliver specific pore size producing dope to the other two slotdies.

As illustrated in FIG. 2, in yet another possible configuration of thesystems and methods of the present application, one vessel could providea mother dope to one Dial-A-Por™ unit 140 for thermal manipulation to aspecific temperature to produce a specific pore size then deliver the somanipulated dope to two slot dies 128, 130 by providing a system 260including a split transportation means 210 having branches 212, 214,connected to slot dies 128, 130, respectively.

As can be seen, the permutations and combinations of the systems andmethods for producing the reinforced, three-zone microporous membrane inaccordance with the systems and methods of the present application arequite numerous.

As illustrated in FIG. 5, in order to manufacture the three-zonemicroporous membrane, the support material 102 having first 104 andsecond 106 sides is impregnated with the first dope 108 from theappropriate dope source by any of a variety of techniques, e.g., rollcoating, spray coating, slot die coating, and the like, with slot diepressure impregnating being presently preferred, to substantiallycompletely impregnate the support material 102 with the first dope 108.As used in this disclosure, “complete impregnation of the supportmaterial” means that all fibers of the support material are completelysurrounded by liquid dope and that no portion of the support material isnot covered by liquid dope and that no portion of the support materialprotrudes from the center zone into either the second or third zones inthe finished three-zone membrane.

The specifics of the production of the reinforced, three-zonemicroporous membrane is discussed in detail in the '816 and the '797applications and further discussion here is believed to be unnecessary.

In accordance with one preferred embodiment, the second 110 and third116 dopes (see FIG. 5) provided from appropriate dope sources, includingthe same mother dope source, produce substantially identical pore sizesbut produce a different pore size than the first dope 108, provided fromthe appropriate source, including the same mother dope source of thesecond and third dopes. In accordance with another preferred embodiment,the second 110 and third 116 dopes provided from appropriate dopesource, including the same mother dope source, produce a different poresize as well as each producing a different pore size from the first dope108 provided from an appropriate dope source, including the same motherdope source. It is possible to have any pore size from the largest tothe smallest in any of the three zones and in any order.

In one presently preferred embodiment, the middle zone 120 (asillustrated in FIG. 7) of the microporous membrane 101 should have anaverage pore size which is at least about twenty percent (20%) greater,preferably at least about fifty percent (50%) greater, more preferablyat least about 100% greater, and most preferably at least about 120%greater, than the average pore size of at least one of the upper zone122 and lower zone 124 of the membrane and preferably both the upper andlower zones. The pores formed in the middle zone 120 have an averagesize of about ten (10) microns or less and the average pore size willpreferably range from about 0.5 microns to about two (2) microns, morepreferably from about 0.1 to about one (1.0) microns. The middle zone120 has a pore size distribution which is preferably quite narrow inrange, although this is not essential for satisfactory performance.

The middle zone 120 should be as thin as possible so long as it providessufficient structural strength and embeds the support material 102 suchthat, presently preferably, no fibers of the support material protrudefrom the middle zone 120 into either the upper 122 or the lower 124zone. However, in one presently preferred embodiment, somestrands/fibers of the support material 102 are contiguous with orslightly protrude into at least the one of the other two zone 122, 124formed from a tight dope or coating solution or into both zones 122, 124when both zones are formed from a tight dope. Most preferably, somestrands/fibers of the support material 102 are contiguous with orslightly protrude into the other two zone 122, 124.

It is believed that having a relatively thin middle zone in which atleast some of the scrim is not completely encapsulated within the middlezone may be advantageous in that the thickness of the middle zone willbe kept to a minimum, thus, resulting in a thinner overall finishedmembrane. The thickness of the middle zone will typically range fromabout fifty (50) microns to about one hundred fifty (150) microns andpreferably from about seventy-five (75) microns to about one hundred(100) microns or whatever dope volume is necessary to substantiallyimpregnate the scrim being impregnated at any specific time.

In one presently preferred embodiment which would result from the systemand methods of the present application, the upper 122 and the lower 124zones of the microporous membrane 101 possess pores which have a sizeproviding the desired filtration efficiency or particle removal.Generally, the average size of the pores of the upper zone and the lowerzone will be about one (1) micron or less, and can typically range fromabout 0.01 microns to about one (1) microns. More preferably, theaverage size of the pores of each zone will range from about 0.2 micronsto about 0.5 microns. This zone microporous membrane is preferablynarrow. In a particularly preferred embodiment, the average pore size ofthe upper zone is substantially the same as the average pore size of thelower zone. By “substantially the same,” it is meant that the averagepore size of the upper zone does not differ from that of the lower zone,and vice versa, by more than about twenty-five (25%) percent.

One important feature of one preferred embodiment of the reinforced,three-zone microporous membrane 101 (see FIG. 7) produced by the systemsand methods of the present application is that the upper and the lowerzones have substantially the same thickness so as to provide geometricsymmetry around the central axis of the membrane. These zones should beas thin as possible in order to minimize the pressure drop across thereinforced, three-zone microporous membrane while being sufficientlythick to yield desired particulate removal. The individual thickness ofeach of the upper and lower zones will generally range from abouttwenty-five (25) microns to about one hundred (100) microns, preferablyfrom about thirty-five (35) microns to about sixty (60) microns. Theoverall thickness of the reinforced, continuous, monolithic,geometrically symmetrical, microporous filtration membrane that would beproduced by the system and method of the present application willgenerally not exceed about ten (10) mils.

The geometric symmetry of the microporous membrane produced under thesystems and methods of the present application should minimizemechanical strains, reduce the likelihood of zone/layer separation ofthe three-zone membrane and generally improve the structural integrityof the three-zone membrane. These features are particularly important tofan-fold pleated cartridge arrangements, where both sides of themicroporous membrane are expected to bend equally well around theneutral (unyielding) axis of the reinforcing scrim. Such bending shouldresult in an equal distribution of tension and compression forces in thepleat crests and troughs, such that neither side is burdened with anexcessive tension or compression load, which would increase thepossibility of damage and/or breech failure of the membrane at the pleatarea. Furthermore, the unique thin cross-section, on both sides, of thethree-zone membrane that would be produced using the systems methods ofthe present application should provide an advantage, in that the tensionand compression forces should be minimized as the absolute radius fromthe center of the reinforcement to the outside surface of the three-zonemembrane is minimized. However, it should be understood that thethickness of one of the upper or the lower zone could be considerablythicker than the other and still be within the teachings of the systemsand methods of the present application.

The reinforced microporous three-zone membrane may be rolled and storedfor use under ambient conditions. It will be understood that thereinforced, three-zone microporous membrane produced in accordance withthe systems and methods of the present application may be formed intoany of the usual commercial forms, such as, for example, discs orpleated cartridges.

For sterile filtration involving biological liquids, the reinforced,three-zone microporous membrane is sanitized or sterilized byautoclaving or hot water flushing. The reinforced, three-zonemicroporous membrane produced by the systems and methods of the presentapplication should prove resistant to this type treatment, particularlywhen a hydrolytically stable nylon is used as described hereinabove, andretains its structural integrity in use under such conditions.

The reinforced, three-zone microporous membrane produced by the systemsand methods of the present application should be easy to handle andreadily formed into convoluted structures, e.g. pleated configurations.By reason of its improved flow characteristics, it should be capable ofbeing employed directly in existing installations, without pumpingmodifications. Specifically, due to the improved flow rate, the existingpumps should actually operate at lower loads and thus would most likelyhave longer useful lives.

The reinforced, three-zone filtration membrane produced in accordancewith the systems and methods of the present application should becharacterized by unexpectedly high flow rates for a given differentialpressure and also characterized by durability, strength, uniformity,lack of pinholes and bubble defects. In many applications, the preferredmembranes could be used with either side of the membrane facingupstream.

As should be clear from the foregoing, the utilization of the originalDial-A-Por™ unit, as illustrated in FIG. 3, has undergone considerableevolution since the development of the initial Dial-A-Por™ unit shown inFIG. 3. As discussed above, the system 310 of FIG. 3 included anindependent metering pump 24 operatively positioned prior to theDial-A-Por™ unit including the thermal manipulation means 26, 32 forpumping the dope from the vessel 12 through the various thermalmanipulation means and to reservoirs. The reservoirs were thenoperatively connected to a specific die, as illustrated in FIG. 5. Asdescribed above, the thermally manipulated dope was then moved from thereservoir to each respective die utilizing a metering pump tocontrollably deliver the dope to the respective die at the requiredpressure for applying the thermally manipulated dope to the scrim.

During the evolution from the single Dial-A-Por™ unit to the multipleDial-A-Por™ unit of the present application, alternative dope movingmeans or systems were developed. As described earlier with respect topatent application Ser. No. 09/022,295, the vessel was typicallymaintained in an inert nitrogen atmosphere from about zero (0) to aboutfifty (50) psig. The high end of the pressure developed by the inertnitrogen atmosphere was found sufficient to move the dope from thevessel to and through the Dial-A-Por™ units and to the inlet of themetering pumps which were operatively connected to each of the dies.Thus, the metering pump 24 of the original Dial-A-Por™ unit (see FIG. 3)was not required when multiple Dial-A-Por™ units were operativelyconnected to the Vertical Coating Line of FIG. 5.

While a plurality of possible pressure and pumping systems and variouscombinations thereof have been found to be operative, one key tosuccessfully operating the multiple Dial-A-Por™ system 10 of the presentapplication is to provide sufficient pressure or force to move the dopeto and through the Dial-A-Por™ units, regardless of the pressure sourceor dope moving means, and to specifically control the amount of dopedelivered to each die.

As illustrated in FIG. 8, one presently preferred multiple Dial-A-Por™unit 10 includes the vessel 12 being pressurized to a sufficiently highpressure, presently preferably, about forty-five (45) psig. The dope ismoved from the storage vessel to and through each specific Dial-A-Por™unit(s) 25, 140, 142 via the pressure on the vessel. After the dope hasbeen thermally manipulated, by one, two or three Dial-A-Por™ units, thethermally manipulated dope moves by the pressure to the inlet of a flowcontrol valve, a metering pump or other precision flow control device,such as, for example, the presently preferred metering pump availablefrom Roper, Pump Company, model No. X5SS1PTY9JOLW, Type I, which thenmoves the dope to each die. The metering pumps 400, 402, 404 areeffective to controllably deliver the appropriate amount of thethermally manipulated dope to the respective dies 126, 128, 130 at theappropriate rate. The metering pumps or the flow control devices arespecified and selected based upon the precision flow controlrequirements for a specific application.

In the presently preferred multiple Dial-A-Por™ unit configuration, eachdie has its own flow control device or metering pump 400, 402, 404. Theflow control devices or metering pumps 400, 402, 404 control the deliverof the thermally manipulated dope to each of the dies 126, 128, 130,respectively, with the desired amount of thermally manipulated dope forapplication to the scrim needed to properly form the desired threephase, reinforced, microporous membrane at the dope processing site 14.

One of the many possible alternatives to this specific systemarrangement or configuration includes operatively positioning valvesbetween each metering pump and each die for diverting the thermallymanipulated dope from the dies to a waste container 410, 412, 414 orback to a previous location in the process, such as, for example, priorto or after the diversion valves 192, 196, 200.

Thus, in the presently preferred multiple Dial-A-Por™ system 10, one ormultiple storage vessels are pressurized to about forty-five (45) psigfor moving the dope from the vessel to one, two or three Dial-A-Por™units under sufficient pressure to move the thermally manipulated dopeto the inlet of a flow control or metering pump 400, 402, 404. Themetering pump for each die then controllably delivers the thermallymanipulated dope to each die at a rate appropriate for each of the zonesof the specific three-zone reinforced microporous membrane beingproduced.

As illustrated in FIG. 9, a metering pump can be positioned with each ofthe Dial-A-Por™ units, similar to the original Dial-A-Por™ unit of FIG.3, and provide the pressure or force necessary to move the thermallymanipulated dope all the way from the vessel(s) 12, 152, 154 to each die126, 128, 130 without the incorporation of any other flow or meteringpumps between each Dial-A-Por™ unit and the respective die (see FIG. 8).However, one potential disadvantage of this particular systemconfiguration is that the Dial-A-Por™ unit(s) will be subjected to thehigher pressures required to provide the thermally manipulated dope toeach die and, thus, the specification for each of the components of theDial-A-Por™ unit(s) would most likely require higher cost componentsthan would the system components using the presently preferred method ofmoving the dope from the vessel through the Dial-A-Por™ under pressureto the inlet of metering pumps for application to the scrim, as ispresently preferred.

Another possible alternative multiple Dial-A-Por™ system is illustratedin FIG. 10. In this alternative system, the flow control pumps ormetering pumps 400, 402 and 404 and the recirculation systems and wastecollection vessel system of FIG. 8 are utilized, but the metering pumpsof FIG. 3 are replaced by fluid transport pumps (not shown) whichessentially replace the pressure provided by pressurizing the vessel 12described above. The fluid transport pumps are used to move the dopefrom the storage vessel, which must be under sufficient pressure to movethe dope from the vessel to the inlet of the fluid transport pump,through the Dial-A-Por™ units to the individual flow control units, suchas, for example, a flow control valve or metering pumps for each die.

This alternative system has several disadvantages. If a flow controlvalve is utilized, then the Dial-A-Por™ units would be subjected to thehigher pressures required at the dies and a more complicated flowcontrol system would be required to meter the flow to the dies. If themetering pumps are inserted between the Dial-A-Por™ units and the dies,the system will become more complicated in that a control system wouldbe required to balance the pressures between the two pumps in series.

An additional possible alternative of many possible alternatives wouldbe to position one fluid transport pump 450 between the primary storagevessel and the fluid transportation system 144. In this alternativesystem, only one fluid transport pump 450 would be used to move the dopefrom the vessel to and through the Dial-A-Por™ unit(s) to the inlet portof one, two or all three of the metering pumps or flow control valvespositioned between each Dial-A-Por™ unit(s) and its respective die.

As above, there are several disadvantages. If a flow control valve isutilized, then the Dial-A-Por™ units would be subjected to the higherpressures required at the dies and a more complicated flow controlsystem would be required to meter the flow to the dies. If the meteringpumps are inserted between the Dial-A-Por™ units and the dies, thesystem will become more complicated in that a control system would berequired to balance the pressures between the two pumps in series.

As illustrated in FIG. 11, in yet another of a plurality of possibleconfigurations of the systems and methods of the present application,one vessel could provide a mother dope to one Dial-A-Por™ unit 140 forthermal manipulation to a specific temperature to produce a specificpore size then deliver the so manipulated dope to the two slot dies 126,128 via a system 260 including a split transportation means 210 havingbranches 213, 214, operatively connected to slot dies 126, 128,respectively. It is understood that the flow to each die must becontrolled in some manner, as discussed above.

From the foregoing descriptions, it should now be readily apparent thatthe systems of the present application can be adapted to provide for themanufacture of a plurality of possible three zone, reinforcedmicroporous membrane. One key is that whatever means are utilized formoving the dope from the pressurized storage vessel(s) through one, twoor three Dial-A-Por™ units must be effective to provide a sufficientvolume of the thermally manipulated dope either to the inlet of a flowcontrol device, such as, for example, a flow control valve or a meteringpump for controlling the amount of thermally manipulated dope to bedelivered to each die or must be effective to controllably deliversufficient amounts of the thermally manipulated dope directly from thestorage vessel to and through the one, two or three Dial-A-Por™ units toeach individual die so as to enable sufficient dope to be applied to thescrim from each die during the manufacturing process at the dopeprocessing site.

As stated above, the presently preferred system for both a single and amultiple Dial-A-Por™ system includes pressurizing the vessel to aboutforty-five (45) psig, which has proven sufficient to move the dope fromone vessel through three Dial-A-Por™ units to three metering pumps, onemetering pump between each Dial-A-Por™ unit and each die, and thenutilizing the metering pumps to control the transfer of the thermallymanipulated dope to each die for application of the dope to the scrim atthe dope processing site.

PROPHETIC EXAMPLES

The following examples are directed to the production of reinforced,three-zone microporous membrane including the preparation of a motherdope, thermal manipulation of the mother dope to produce a dope thatwhen applied to a scrim by dope application mechanism or means providesany one of a plurality of possible specific pore sizes in a specificperformance zone of the final microporous membrane, the delivery of thedope to a dope processing site and the application of the dope to formthe membrane at the dope processing site resulting in a reinforced,three-zone microporous membrane.

Until recently, mother dopes have been produced as described in U.S.patent application, Ser. No. 09/022,295, U.S. Pat. No. 6,056,529, andreinforced, three-zone microporous membrane has been produced using onlyone dope provided by a Dial-A-Por™ system but no reinforced, three-zonemicroporous membrane had been produced using the preferred systems andmethods of the present application. The following two prophetic Examplesdescribe how such reinforced, three-zone microporous membrane would beproduced using the preferred systems and methods of the presentapplication.

Prophetic Example 1

A mother dope of approximately a fourteen and one-half percent (14.5%)by weight Nylon 66 (Monsanto Vydyne 66Z), approximately seventy-sevenand four-tenths percent (77.4%) by weight Formic Acid and approximatelyeight and one-tenth percent (8.1%) by weight methanol, is produced bythe method disclosed in U.S. Pat. Nos. 3,876,738 and 4,645,602. Anothermethod for producing such dopes is described in European PatentApplication No. 0 005 536 to Pall.

The dope is processed in a vessel to a maximum temperature of about 28°C., after the nylon is added to the mixture, which should result in aFAOP of about 196 psi and a IBP of about 149.3 psi. The storage vesselcontaining the above mother dope is operatively connected to the threeseparate Dial-A-Por™ unit for thermal manipulation of portions of themother dope. Then the vessel is pressurized to approximately forty-five(45) psi with nitrogen, to move the dope from the vessel to each of theDial-A-Por™ units, each Dial-A-Por unit is connected to precisionmetering pumps to feed precise amounts of treated dope to one of each ofthe three coating dies.

Each Dial-A-Por™ unit or system for thermal manipulation (elevation ofthe dope temperature to a predetermined temperature) is activated andthe target temperature is set to the specific target temperature for thedope to be delivered to each slot die. When the two heating mechanism ormeans and the cooling mechanism or means reached their respective targettemperatures, dope valves are opened and dope is moved by pressure fromthe sealed vessel through each Dial-A-Por™ system, then on to precisionmetering pumps and the respective coating dies.

Since the results of the tests disclosed in the '295 application showedthat the target temperature control of Tmax critical was accomplished toabout 0.15° C. below the ±0.2° C. target, and the thermal responsetesting generated smooth and repeatable curves, it was established thatthe dope/membrane material properties resulting from the Dial-A-Por™systems were precise and repeatable.

Thus, at this point in our examples, we have merely described thepreparation of a mother dope and the thermal manipulation of the motherdope to provide one of a plurality of possible pore size producing dopesafter the controlled thermal manipulation.

Once portions of the mother dope are thermally manipulated to a specificpore-size-producing dope temperature and cooled to an appropriateprocessing temperature, each thermally manipulated dope is deliveredpreferably via one precision metering pump described above from arespective Dial-A-Por™ unit to the selected one of the three slot diesof the apparatus at the dope processing site as described above and inU.S. patent application Ser. Nos. 09/040,979 and 09/040,816, now U.S.Pat. Nos. 6,264,044 and 6,090,441, to produce a geometrically symmetricand pore size symmetric reinforced, three-zone membrane with an “open”(large pore size) scrim encapsulated center zone.

At the dope processing site, non-woven Polypropylene bicomponent fiberweb or scrim suitable for preparation of the reinforced, three-zonemembrane (commercially available from Freudenberg under the tradenameViledon®, Grade #F02432), having a basis weight of nominally 30gm/sq.meter is processed by the method taught in the Ser. Nos.09/040,979 and 09/040,816 applications, now U.S. Pat. Nos. 6,264,044 and6,090,441. The scrim is pre-treated with a mild Corona Discharge toenhance its wetability prior to being pressure impregnated. The largerpore size dope is provided from the Dial-A-Por™ unit operativelyconnected to the first slot die (impregnating die) and is used topressure impregnate the scrim, with an impregnation weight of aboutseven (7) gm/sq.meter of Nylon solids. The nylon solids are providedfrom the dissolved nylon in the dope solution, which can be, forexample, a fourteen and one-half (14.5) wt % nylon solution(approximately 50 grams of liquid dope per square meter), which issufficient to impregnate and fill the void volume of the scrim, creatingthe first zone of large pore size dope integral with the supportingscrim.

Almost immediately following the pressure impregnation of the scrim withthe dope from the first slot die, both sides of the pressure impregnatedscrim are essentially simultaneously coated with substantially evenlayers of a smaller pore size dope received from the second and thirdDial-A-Por™ units, respectively. In this example, the total coatingweight delivered to the two sides is about thirty-seven (37) gm/sq.meterof Nylon solids in about a fourteen and one-half (14.5) wt % solution(approximately 260 grams of liquid dope per square meter), with thetotal being split between the two streams of dope feeding onto the twosides of the pressure impregnated scrim, so that both sides aresubstantially evenly coated with the two streams of dope which have beenseparately processed thorough their respective Dial-A-Por™ units tosubstantially the same end-point of maximum temperature for producingsubstantially equivalent small pore size membrane upon coating andquenching. These should create the second and third zones of thefinished membrane from the small pore size dope. The grand totalapplication of both dopes (large and small pore size) is, thus,approximately forty-four (44) gm/sq.meter Nylon solids. The thus coatedthree-zone structure is then quickly brought into contact with aMarinacco-style quench solution, which simultaneously quenches thethree-zone structure from the outer surfaces of the small pore sizedope, such that a continuous microporous membrane structure is formed.The quenched membrane is then washed, dried under X & Y directiondimensional restraint, and tested, in the usual manner.

Prophetic Example 2

A second three-zone membrane is prepared in nearly identical manner asin Example 1, with the exception that one of the coating sides of thepressure impregnated scrim (in this case, Zone Two) is coated with dopefrom it's respective Dial-A-Por™ unit which had been processed tosubstantially the same end-point of maximum temperature for producingsubstantially equivalent large pore size membrane as the dope processedfrom the Zone One (impregnating zone) Dial-A-Por™ and slot diecombination. Zone Two is thus coated with approximately fifteen (15)gm/sq.meter Nylon solids from the large pore size dope produced by itsrespective Dial-A-Por™ units or alternatively having the Zone OneDial-A-Por™ unit provide the same dope. The opposite side (Zone Three)is simultaneously coated with the approximately twenty-two (22)gm/sq.meter Nylon solids from small pore size received from theappropriate Dial-A-Por™ unit. After two-side simultaneous quenching,washing and restrained drying, the resultant finished membrane wouldachieve a continuous, substantially geometric symmetry around theneutral axis of the reinforcing scrim, but have very different pore sizeattributes on both sides of the scrim. (i.e., Pore Size Asymmetric).

Discussion of the Prophetic Examples

As can be seen in Table II of the Ser. No. 09/040,979 and the Ser. No.09/040,816 applications, now U.S. Pat. Nos. 6,264,044 and 6,090,441, theExample 1 membrane produced in accordance with the systems and methodsof the present application should show a clearly improved flow rate overthe standard (control) membrane as disclosed in those applications. Itis believed that a similar membrane produced in accordance with thesystems and methods of the present application would also have a clearlyimproved flow rate over a standard (control membrane) of the sameapplication.

The raw water flow rate (Q, expressed as cc/min clean deionized waterfor a nominally forty-seven (47) mm test disc (13.5 cm² test area) underwater pressure of 5 psid) should show about a twenty (20%) percentimprovement, while the integrity, as measured by Initial Bubble Point,should be surprisingly increased by about six (6%) percent, for the sameoverall membrane thickness. This expected improvement potentially shouldprovide a double benefit, these being improved clean water flow rate andimproved integrity as measured by IBP. The increase in Initial BubblePoint should be corroborated by both the increase in membraneFoam-All-Over-Point, and the decrease in the ASTM Mean Flow Pore sizerating.

The Example 2 membrane should provide a stunning improvement in flowrate over the standard (control) membrane as disclosed in thoseapplications of about seventy-eight (78%) percent, while retainingalmost the same integrity attributes in IBP and FAOP. The Mean Flow Pore(MFP), a more universally recognized method for mean pore size, of whichFAOP is attempting to approximate, should show the expected difference:a larger mean flow pore is consistent with a higher flow rate, and thisindicates that there is, by the flow averaging method, a widerdistribution of pore sizes in the Example 2 membrane if it were comparedto a control membrane. This should not, however, diminish the importanceof the flow improvement with essentially the same Initial Bubble Point,which is a rating of the single largest pore on the membrane, and ameasurement which the microfiltration industry has come to rely upon fortesting the integrity of a membrane. Thus, Example 2 could illustrateanother advantage to the membrane produced in accordance with thesystems and methods of the present application, which is the ability toproduce, in a single membrane, three separate zones of performancewhich, when oriented by decreasing pore size, can provide a novel,surprisingly thin section combination reinforced prefilter and finalfilter, having geometric symmetry, good integrity, and very high flowrates.

Summary of the Prophetic Examples

The systems and methods of the present application for producingreinforced, three-zone membrane should provide microporous membranehaving markedly improved flow rates in filtration applications, fortheir pore size attributes, as compared to standard products now commonin the membrane filtration industry. The relatively thin cross-sectionsof these three-zone membrane products should result in membranecartridges having more surface area and even higher throughputs. Thiscombination should translate into a higher value added product for thefiltration customer.

The resultant three-zone microporous membrane was composed of threezones that were continuously joined by the molecular entanglement of thepolymers which occurred in the liquid state of the dope after each ofthe outer zone dopes was coated onto the dope of the central zone andprior to quenching. This is significantly different from the prior artlamination process wherein three separately formed membranes werequenched and then laminated together. Thus, it is clear that the liquidto liquid mixing of the central zone liquid dope with each of the outerzones liquid dope, prior to quenching, resulted in a three phase,reinforced, microporous membrane having a continuous polymerentanglement on the molecular level, as illustrated by the scanningelectron photo micrographs.

It is believed that routine experimentation with substrates,pre-treatments, zone coating weights, polymers, dope viscosity,thickness, pore sizes, and orientations of the zones with respect topore sizes will yield optimized membrane products which would havesuperior performance to existing membrane products. Other membraneapplications which will benefit from the ability to customize zoneperformance will include (as examples), diagnostic products using bodyfluids, transfer membranes, separation devices, medical devices, andothers which will become obvious to those skilled in the arts ofmembrane science.

Based on the above, it should be clear that the teachings of the presentapplication which includes the use of at least one mother dope batchprocessed through at least one and as many as three separate Dial-A-Por™units to deliver different pore size producing dope to an appropriateapplication mechanism or means for application first to a scrim and thento each side of the dope impregnated scrim to induce the interminglingof the different dope applications provided in fluid form from the threedies prior to quench provides the three-zone, continuous membrane, asdescribed in the aforementioned patent applications.

ACTUAL EXAMPLES

The actual following examples are directed to the production ofreinforced, three-zone microporous membrane including the preparation ofa mother dope, thermal manipulation of the mother dope to produce a dopethat when applied to a scrim by dope application mechanism or meansprovides any one of a plurality of possible specific pore sizes in aspecific performance zone of the final microporous membrane, thedelivery of the dope to a dope processing site and the application ofthe dope to form the membrane at the dope processing site resulting in areinforced, three-zone microporous membrane.

Until recently, mother dopes have been produced as described in U.S.patent application Ser. No. 09/022,295, U.S. Pat. No. 6,056,529, andreinforced, three-zone microporous membrane has been produced using onlyone dope provided by a Dial-A-Por™ or system for thermal manipulation(elevation of the dope temperature to a predetermined temperature) butno reinforced, three-zone microporous membrane had actually beenproduced using the preferred systems and methods of the presentapplication. The following actual Examples describe how such reinforced,three-zone microporous membrane have been produced using the preferredsystems and methods of the present application.

Actual Example 1

A mother dope, identified as Dope #00B027, of about fourteen andone-half percent (14.5%) by weight Nylon 66 (Monsanto Vydyne 66Z), aboutseventy-seven and four-tenths percent (77.4%) by weight Formic Acid andabout eight and one-tenth percent (8.1%) by weight methanol, wasproduced by the method disclosed in U.S. Pat. Nos. 3,876,738 and4,645,602, the disclosure of each is herein incorporated by reference.

The dope was processed in a vessel to a maximum temperature of abouttwenty-eight degrees (28°) C., after the nylon was added to the mixture,and allowed to mix as per the normal cycle. It was believed that thetemperature control equipment which maintains the maximum temperaturethrough this mother dope mix cycle was not as precise as the Dial-A-Por™system's temperature regulation; and may typically vary by as much asabout ±0.5 degrees C. or more. This will affect the ability to preciselyreplicate the characteristics of a given mother dope, even when the sameformulation was repeated.

To gain an appreciation of the pore size of a microporous nylon membranecast directly from this mother dope, a small portion (˜100 cc) of themother dope was cast and quenched in a laboratory apparatus whichsimulates the casting process described in U.S. Pat. No. 3,876,738, toMarinaccio and Knight, to produce a nominally five (5) mils thick wet,non-reinforced layer of microporous nylon membrane. This membrane waswashed in deionized water, then folded over onto itself, about ten (10)mils wet, and dried under conditions of restraint to prevent shrinkagein either the machine direction (x-direction) or cross direction(y-direction). This produced a small sample of dried double layernon-reinforced microporous nylon membrane having a combined thickness ofabout five (5) mils after shrinkage in thickness (z-direction) of thecollapsing wet pore structure was complete.

An Initial Bubble Point test was attempted, as described in U.S. Pat.No. 4,707,265, using deionized water as a wetting fluid. The resultingmembrane pore structure was so tight (i.e. small pores), that theInitial Bubble Point was higher than the measurement system gauge couldread (>100 psig).

A second small portion of the mother dope was cast, quenched, foldedonto itself, then dried under restraint to produce a substantiallyidentical sample as described above. This sample was wetted in asolution containing about sixty percent (60%) by weight IsopropylAlcohol and about forty percent (40%) by weight deionized water. Thissolution has a lower surface tension than that of pure water, thusproviding a reduction in capillary expulsion pressure needed to performthe Initial Bubble Point test. The approximate surface tension of the60/40 IPA/H₂O mix is about twenty-four (24) dyne/cm, where as thesurface tension of pure DI water is about seventy-three (73) dyne/cm.The test was performed, and Initial Bubble Point pressure was recordedas about fifty-four (54) psig in Isopropyl Alcohol.

Because the surface tension of the wetting fluid is directlyproportional to the measured bubble point pressure, it is estimated thatthe effective Initial Bubble Point of such a membrane would be about afactor of three times (3×) greater if tested in pure water, or aboutone-hundred-sixty-two (162) psig in pure water. By industry convention,such a nylon microporous membrane might be rated as nominally about0.02μ to about 0.04μ in pore size. This was evidence that the motherdope, as formulated and produced for this example, had a very small poresize prior to being processed by each Dial-A-Por™ unit, and furtherprocessed into a three-zone microporous nylon membrane by a verticalcasting apparatus at a dope processing site.

After the above tests, the storage vessel containing the above motherdope was operatively connected to the three separate Dial-A-Por™ unitsfor thermal manipulation of portions of the mother dope. Then, thevessel was pressurized to about forty-five (45) psi with nitrogen, tomove the dope from the vessel to each of the Dial-A-Por™ units, eachDial-A-Por™ unit was operatively connected to a precision metering pumpfor transporting precise amounts of thermally manipulated dope to arespective one of each of the three coating dies.

Each Dial-A-Por™ unit or system for thermal manipulation (elevation ofthe dope temperature to a predetermined temperature) was activated andthe target temperature was set to the specific target temperature forthe dope to be delivered to each of the three slot dies. When the twoheating mechanisms or means and the cooling mechanisms or means reachedtheir respective target temperatures, dope valves were opened and dopewas moved under pressure from the sealed vessel through each Dial-A-Por™unit, then on to each precision metering pump and each respectivecoating die.

The specific target temperatures for each of the three Dial-A-Por™units, feeding the respective Membrane Zones, was as follows:

Membrane Zone One (the impregnation zone of the reinforcing substrate orscrim), the target maximum temperature was fifty-four degrees (54.0°) C.to effect a relatively lower bubble point impregnation dope attribute,followed by cooling to about twenty-one degrees (21°) C., to effect auseful dope viscosity for impregnation and coating.

Membrane Zone Two, (the coating zone applied on the same side or “near”side of the reinforcing substrate as the impregnation die), the targetmaximum temperature was fifty-four degrees (54.0°) C. to effect arelatively lower bubble point coating on the Membrane Zone Two side,which was substantially the same as the bubble point of the impregnationzone, followed by cooling to about twenty-one degrees (21°) C., toeffect a useful dope viscosity for coating.

Membrane Zone Three (the coating zone applied on the opposite side ofthe reinforcing substrate from the impregnation die), the target maximumtemperature was forty-five degrees (45.0°) C., to effect a relativelyhigher bubble point coating in the Membrane Zone Three side, followed bycooling to about twenty-one degrees (21°) C., to effect a useful dopeviscosity for coating. Since the Membrane Zone Three side contains therelatively higher bubble point as compared to the (substantially equal)bubble points of the Membrane Zone One and Membrane Zone Two sides, theproduct produced for this example will be a geometrically symmetric,pore size asymmetric nylon microporous membrane.

At this point in our example, we have described the preparation of amother dope, and the thermal manipulation of the mother dope to provideone of a plurality of possible pore size producing dopes after thecontrolled thermal manipulation.

Once portions of the mother dope were thermally manipulated to aspecific pore size producing dope temperature and cooled to anappropriate processing temperature, each thermally manipulated dope wasdelivered preferably via one precision metering pump described abovefrom a respective Dial-A-Por™ unit to the selected one of the three slotdies of the apparatus at the dope processing site as described above andin U.S. patent applications Ser. Nos. 09/040,979 and 09/040,816, nowU.S. Pat. Nos. 6,264,044 and 6,090,441 to produce a geometricallysymmetric and pore size asymmetric reinforced, three-zone membrane witha first “open” (large pore size) scrim encapsulated center zone(Membrane Zone One), and one “open” (large pore size) outer zone on oneof the sides of the scrim (Membrane Zone Two), and one “tight” (smallpore size) outer zone (Membrane Zone Three) opposite the other outerzone.

At the dope processing site, non-woven Polypropylene bicomponent fiberweb or scrim suitable for preparation of the reinforced, three-zonemembrane (commercially available from Freudenberg under the tradenameViledon®, Grade #F02432), having a basis weight of nominally 30gm/sq.meter was processed by the method taught in the Ser. Nos.09/040,979 and 09/040,816 applications. The scrim was pre-treated with amild Corona Discharge to enhance its wetability before being pressureimpregnated. The relatively larger pore size dope, was provided from theDial-A-Por™ unit operatively connected to the first slot die (orMembrane Zone One impregnating die) and was used to pressure impregnatethe scrim, with an impregnation weight of about twelve and one-half(12.5) gm/sq.meter of Nylon solids. The nylon solids were provided fromthe dissolved nylon in the dope solution, which were, in this example, afourteen and one-half (14.5) wt % nylon solution (about eighty-six andtwo-tenths, 86.2, grams of liquid dope per square meter), which wassufficient to impregnate and fill the void volume of the scrim, andleave a small excess of coating dope on the application side of thescrim creating the first zone of large pore size dope integral with thesupporting scrim.

Within a short distance of travel following the pressure impregnation ofthe scrim with the dope from the first slot die, both sides of thepressure impregnated scrim were essentially simultaneously coated withdope received from the other two slot dies, which was provided fromtheir respective Dial-A-Por™ units, as described above.

Membrane Zone Two was thus coated with about thirteen (13.0) gm/sq.meterNylon solids from the large pore size dope produced by its respectiveDial-A-Por™ unit. Membrane Zone Two was applied from the same side ofthe scrim as the impregnation die, i.e. both dies for Membrane Zone Oneand Membrane Zone Two (near) faced the same direction. Membrane Zone Twocontained dope that was substantially the same bubble point as theimpregnation zone (Membrane Zone One). Because there was a small excessof dope carrying down the (Membrane Zone One oriented application die)face of the scrim, the Membrane Zone Two application weight was loweredrelative to Membrane Zone Three, in order to maintain geometricsymmetry. The opposite side (Membrane Zone Three) was substantiallysimultaneously coated with the about eighteen and one-half (18.5)gm/sq.meter Nylon solids from the small pore size dope received from itsrespective Dial-A-Por™ unit. The total coating weight from all dies thusapplied to the scrim was about forty-four (44) gm/sq.meter. Aftertwo-side simultaneous quenching, washing and restrained drying, theresultant finished membrane achieved a continuous, substantiallygeometric symmetry around the neutral axis of the reinforcing scrim, buthad very different pore size attributes on both sides of the scrim.(i.e., Pore Size Asymmetric).

The resultant three-zone, geometrically symmetric, pore size asymmetricnylon microporous membrane of this Actual Example One had the measuredattributes as illustrated in Table 1. For illustration, the three-zoneasymmetric pore structure is shown in cross section by Scanning Electronmicrograph in FIGS. 12a-b.

Description of the Attribute Measurements made on the membrane asreported in Table 1 are as follows:

Membrane I.D.: The production identification of a specific roll ofmembrane.

Coating Weight: The coating weight delivered to each of the threeseparate zones was given, which was calculated directly from themeasured volumetric flow rate delivered by each zone pump, spread overthe moving web at the process casting width. The total of all zones wasthe expected coating weight for the finished product.

FFBP (60/40 IPA wet): This test is a variant of the K-sub-L test whichhas been promoted by the PALL® corporation as a measurement of poresize, and is described in PALL® literature and validation guides. Here,the knee location was found, using a wetting fluid which was about sixtypercent (60%) by weight Isopropyl alcohol, and about forty percent (40%)by weight water. This measurement was applied to the same in-processsample as was tested for in-process thickness. The value reported was anaverage of two samples; one from the beginning and one from the end ofthe roll.

Thickness: A process gage was used to measure three points across thewidth of a short length of an in-process sample. This sample was takenfrom the wet-as-cast, and DI water washed membrane, in the V/C/Lproduction area. The sample was dried under restraint in crossweb andmachine direction. Three points spanning the crossweb sample are testedwith the process gage, and used to calculate an average which wasreported. The wet-as-cast roll then proceeded to the drying process.

Initial Bubble Point (D.I. water wet): This was a final quality check,and was tested as previously described.

Water Flow Rate: A precision water flow meter was mounted downstream ofa one-hundred-forty-two (142) mm diameter filter disc housing (Milliporesanitary design, Millipore catalogue No. 302200). The housing wasdirectly tapped on the inlet side and the outlet side so that adifferential pressure gage could be used to measure the instantaneousdifferential pressure across the membrane. A precision pressuretransducer was connected across the housing. Fresh filtered 1 megohmD.I. water under pressure, nominally about thirty (30) psi, was plumbedinto the housing with means to regulate flow rate. By varying the cleanwater flow rate through the housing, and measuring the differentialpressure at each flow rate, a pressure vs. flow rate graph wasconstructed. From this, a flow rate was either extrapolated orinterpolated, expressed here in the familiar units of cc/min flow for anequivalent of a forty-seven (47) mm diameter disc, nominally aboutthirteen and one-half (13.5) square centimeter equivalent surface area,at about a five (5.0) psi differential pressure.

Coulter Mean Flow Pore Size: The Coulter Porometer II from Coulterinstruments was used to measure the Mean Flow Pore in accordance withthe instrument manufacturer's instructions, using Porofil wetting fluid,and a thirty-seven (37) mm housing. Three samples were tested, and theaverage value was reported.

Actual Example 2

A second mother dope having the same formulation as described in ActualExample 1 above was prepared, under about the same conditions. The dopewas characterized as before, and the results are also reported inTable 1. Within the limits of common cause error, the dope was areplicate of the Example 1 dope.

A three zone, geometrically symmetric, pore size asymmetric nylonmicroporous membrane was prepared under substantially the sameconditions as described in Actual Example 1. The only substantivedifference was the selection of the specific target maximum temperaturesfor the three separate Dial-A-Por™ units. These specific targettemperatures were as follows. For Membrane Zone One (impregnation), thetarget maximum temperature was fifty-seven degrees (57.0°) C. ForMembrane Zone Two (near side), the target maximum temperature was alsofifty-seven degrees (57.0°) C. For Membrane Zone Three (opposite side),the target maximum temperature was fifty degrees (50.0°) C.

The resultant three-zone, geometrically symmetric, pore size asymmetricnylon microporous membrane was tested and reported in Table 1. Forillustration, the three-zone asymmetric pore structure of this ActualExample 2 membrane is shown in cross section by Scanning Electronmicrograph in FIGS. 13a-b. The resulting membrane has a substantiallylarger pore size rating and a higher clean water flow rate than themembrane of Actual Example 1. This was as expected, considering therelatively higher maximum Dial-A-Por™ unit target temperatures used inthe processing of this membrane.

Actual Example 3

A third mother dope having the same formulation as described in ActualExample One (1) was prepared, under substantially the same conditions asActual Examples One (1) and Two (2). The dope was characterized asbefore, and the results are reported in Table 1. Within the limits ofcommon cause error, the dope was a replicate of the Example One dope.

A three-zone, geometrically symmetric, pore size asymmetric nylonmicroporous membrane was prepared under substantially the sameconditions as described in Actual Example One. The only substantivedifferences are the selection of the specific target maximumtemperatures for the three separate Dial-A-Por™ units. These specifictarget temperatures are as follows. For Membrane Zone One(impregnation), the target maximum temperature was sixty-two degrees(62.0°) C. For Membrane Zone Two (near side), the target maximumtemperature was also sixty-two degrees (62.0°) C. For Membrane ZoneThree (opposite side), the target maximum temperature was fifty-fourdegrees (54.0°) C.

The resultant three-zone, geometrically symmetric, pore size asymmetricnylon microporous membrane was tested and reported in Table 1. Forillustration, the three-zone asymmetric pore structure of this ActualExample Three membrane is shown in cross section by Scanning Electronmicrograph in FIG. 14a-b. It has a substantially larger pore size ratingand a higher clean water flow rate than the membrane of Actual ExampleTwo, and vastly greater than Actual Example One, in any of the commonmeasurements of pore size and throughput. This again demonstrates theexpected effect of higher maximum Dial-A-Por™ temperatures, resulting inlarger pore sizes in each of the separate Membrane Zones. What was alsoclearly illustrated is, that, from substantially identical mother dopes,many different and unique products can be designed and produced by thesemethods and apparatus.

TABLE 1 Mother Dope Characteristics Zone Control Settings Ac- tualInitial Calculated Zone Zone Zone Zone Zone Zone Ex- Mother Dope BubbleIBP 1 (Impreg'n) 2 (Near) 3 (Opposite) 1 (Impreg'n) 2 (Near) 3(Opposite) am- Max Temp. Point (IBP) (= IPA × 3) Target Target TargetCoating Coating Coating ple Membrane (approx) (60/40 IPA) in D.I. H₂OMax. Temp. Max. Temp. Max. Temp. Weight Weight Weight # I.D. Deg.Celsuis psig psig Deg. Celsuis Deg. Celsuis Deg. Celsuis gm/sq. m.gm/sq. m. gm/sq. m. 1 00B027-04 28 54 162 54.0 54.0 45.0 12.5 13 18.5 200B032-04 28 59 177 57.0 57.0 50.0 12.7 13 18.2 3 00B036-02 28 58 17462.0 62.0 54.0 12.5 13.3 19.1 In-Process Measurements Final MembraneMeasurements Total Forward Flow Sheet Initial Water Coulter Actual NylonK-sub-L Thickness Bubble Flow Porosimeter Exam- Coating Bubble Point(Process Point Rate Mean Flow ple Membrane Weight (60/40 IPA) Gage)(D.I. H₂O) (D.I. H₂O) Pore Size # I.D. gm/sq. m. psig mil psig cc/minmicron 1 00B027-04 44 15.3 6.67 40.1 142 0.503 2 00B032-04 43.9 10.97.05 29 231 0.738 3 00B036-02 44.9 8.3 7.46 21.5 483 1.007 *Equilvaentof cc/min @ five (5) psid for a forty-seven mm disc (thirteen andone-half, 13.5, sq, cm.)

Discussion of the Actual Examples

It can be seen from the above examples that a plurality of pore sizescan be effectively produced and placed in specific zones of athree-zone, geometrically symmetric nylon microporous membrane. It isbelieved that anyone of ordinary skill in the art can effectively designpore size symmetric or asymmetric structures, gradient densitystructures, and any one of many application specific structures whilemaintaining geometric symmetry by manipulating the pore sizes, coatingweights, and application temperatures of the zones disclosed in theseactual examples. Other structures are also believed easily realized,having controlled asymmetry in geometry as well.

In the above actual examples, it is believed that the geometricallysymmetric and pore size asymmetric membranes produced have superiorwater flow rates when compared to membranes of equal pore size andintegrity prepared in the traditional manners with a single dope, singlezone design, as had been demonstrated in the previous patentapplications discussed above (U.S. patent application Ser. No.09/022,295, filed Feb. 11, 1998, of Meyering et al., Ser. No.09/040,979, filed Mar. 18, 1998, of Meyering et al. and Ser. No.09/040,816, filed Mar. 18, 1998, of Vining et al., now U.S. Pat. Nos.6,056,529; 6,264,044 and 6,090,441 respectively) examples.

The above described actual examples are taken from real production dataof salable membrane product. The present actual examples are intended todemonstrate reduction to practice of the concept of using threeindependent Dial-A-Por™ units fed from a single mother dope to produce athree-zone, reinforced membrane. Each Dial-A-Por™ unit was operativelyconnected to a unique Zone coating die, and independently processed thesame mother dope to effect different Membrane Zone characteristics, asdesired for the production of many possible unique products from thesame dope formulation. The production of a plurality of possible poresize microporous membranes has now been achieved, using the abovedescribed production equipment The pore size has been simply andeffectively “dialed in” on the production equipment to produce uniqueperformance zones in each of the three zones of the three-zonereinforced membrane through temperature and zone coating weightmanipulation.

Summary of the Actual Examples

The systems and methods of the present application for producingreinforced, three-zone membrane provided microporous membrane havingmarkedly improved flow rates in filtration applications, for their poresize attributes, as compared to standard products now common in themembrane filtration industry. The relatively thin cross-sections ofthese three-zone, membrane products produced membrane cartridges havingmore surface area and even higher throughputs than prior products. Theseproducts clearly translated into a higher value added product for thefiltration customer.

Thus, it should be apparent from the above actual examples that thesystems and methods of manufacturing three-zone, reinforced microporousmembrane has produced a membrane having a minimum functional thicknessand maximum throughput at minimal pressure drops, high integrity and waseconomically produced in any one of a plurality of different pore sizesin each of the three zones. Further, the systems and methods formanufacturing three-zone, reinforced microporous membranes haseliminated the necessity for preparing at least one dope batch accordingto individual unique formulations for each pore size, thus resulting insignificant cost savings and flexibility in the usage of dope batches.

It is believed that routine experimentation with substrates,pre-treatments, zone coating weights, polymers, dope viscosity,thickness, pore sizes, and orientations of the zones with respect topore sizes will yield optimized membrane products which would havesuperior performance to existing membrane products. Other membraneapplications which will benefit from the ability to customize zoneperformance will include (as examples), diagnostic products using bodyfluids, transfer membranes, separation devices, medical devices, andothers which will become obvious to those skilled in the art of membranescience.

Based on the foregoing description, it should now be apparent that theuse of the systems and the methods of the present application to produceany one of the plurality of possible three-zoned, reinforced membranesdescribed herein, and as may be envisioned by those skilled in the art,will carry out the objects set forth hereinabove. It should also beapparent to those skilled in the art that the methods of the presentapplication using the systems of the present application can bepracticed to manufacture a variety of microporous membranes having atleast a single layer of support material at least substantially embeddedin a first zone of microporous membrane and having at least one zone ofmicroporous polymer membrane on each opposed surface of the first zone.Similarly, the dope quench solutions, concentration and temperaturesthereof as well as the speed at which the scrim is continuously fedthrough the apparatus can readily be determined by those skilled in theart.

It is important to note that the three-zone membrane produced by thesystem and methods of the present application will have a discontinuouspore structure with a continuous entanglement of the separatelayers/zones of polymer such that the continuous, reinforced,microporous membrane produced is structurally integral.

After formation of the reinforced, three-zone microporous membrane 101of the present application, the membrane may be treated in accordancewith U.S. Pat. No. 4,473,474, the disclosure of which is hereinincorporated by reference, to produce a cationically charge modifiedmicroporous membrane particularly suitable for the filtration ofparenteral or biological liquid or, in accordance with U.S. Pat. No.4,473,475, the disclosure of which is incorporated herein by referencesto produce cationically charged modified microporous membraneparticularly suitable for the filtration of high purity water requiredin the manufacture of electronic components.

It is believed that experiments can be conducted to verify that thesystems and methods of the present application will have the same, orsimilar results as described herein and in the previously mentionedpending applications or when using other ternary phase inversionpolymers. It is presently believed that the systems and methods of thepresent application can be useful in the processing of a large number ofternary phase inversion polymers into reinforced, three-zone microporousmembrane because of the similar chemical compositions and structures ofthe various phase inversion polymers.

Specifically, since nylon 66 is a member of a group of polymers that arecapable of being processed into microporous membrane via the phaseinversion process, the nature of this process is such that there is astrong probability that the methods and systems of the presentapplication will be applicable to these other polymers as well,including, but not limited to, nylon 66, nylon 46, nylon 6, polysulfone,polyethersulfone, polyvinylidenediflouride (PVDF) and other ternaryphase inversion polymers that form microporous structures through thephase inversion process.

While the systems and methods for making the articles described hereinconstitute preferred embodiments of the invention, it is to beunderstood that the invention is not limited to these precise systemsand methods, and that changes may be made therein without departing fromthe scope of the invention which is defined in the appended claims.

What is claimed is:
 1. A system for manufacturing three-zone microporousmembrane, the system comprising: at least one vessel for containing aternary phase inversion polymer mother dope; a dope processing site; atleast one pressure means, operatively connected to the at least onevessel, and the dope processing site for moving the dope from the atleast one vessel to the dope processing site; a dope transportationsystem, operatively connected to the at least one vessel and the dopeprocessing site, for transfer of the dope from the vessel to the dopeprocessing site; at least one thermal manipulation means, operativelyconnected to the at least one vessel and the dope processing site, fortransforming the dope from the at least one vessel into any one of aplurality of different possible pore size producing dopes; and at leastthree dope application means, operative at the dope processing site andoperatively connected to the at least one thermal manipulation means,for applying the dope at the dope processing site to form three-zonemicroporous membrane.
 2. The system of claim 1 further comprising: atleast a second thermal manipulation means, operatively connected to theat least one vessel, the dope transportation system and at least one ofthe three dope application means, for transforming the dope into any oneof a plurality of different possible pore size producing dopes forapplication at the dope processing site by the at least one of the threedope application means.
 3. The system of claim 2 further comprising: atleast a third thermal manipulation means, operatively connected to atleast one vessel, the dope transporting system and at least another oneof the three dope application means, for transforming the dope into anyone of a plurality of different possible pore size producing dopes forapplication at the dope processing site by the at least a third dopeapplication means.
 4. The system of claim 2 further comprising: bypassmeans, operatively connected to the at least the second thermalmanipulation means, for diverting dope from at least one vessel to thedope processing site such that the dope is not processed by the at leastsecond thermal manipulation means prior to delivery to the dopeprocessing site.
 5. The system of claim 3 further comprising: bypassmeans, operatively connected to at least the third thermal manipulationmeans, for diverting dope from the at least one vessel to the dopeprocessing site such that the dope is not processed by the at leastthird thermal manipulation means prior to being delivered to theprocessing site.
 6. The system of claim 1 further comprising: at least asecond and a third thermal manipulation means, operatively connected tothe at least one vessel and at least two of the three dope applicationmeans respectively, for transforming the dope pumped from the at leastone vessel to the second and the third thermal manipulation means intoany one of a plurality of different possible pore size producing dopesfor application at the dope processing site.
 7. The system of claim 1further comprising: at least a second vessel operatively connected tothe dope transporting means, for containing a ternary phase inversionpolymer dope.
 8. The system of claim 7 further comprising: at least athird vessel, operatively connected to the dope transporting system, forcontaining a ternary phase inversion polymer dope.
 9. The system ofclaim 1 further comprising: bypass means, operatively connected to theat least one thermal manipulation means, for diverting dope beingtransported from the at least one vessel to the dope processing sitesuch that the dope is not processed by the at least one thermalmanipulation means prior to delivery to the dope processing site. 10.The system of claim 1 wherein the thermal manipulation means furthercomprises: heating means, operatively positioned in the at least onethermal manipulation means, for elevating the temperature of at least aportion of the dope to a temperature within about ±0.2° C. of apredetermined temperature, the predetermined temperature being selectedfrom a calibrated characterization curve which describes therelationship between the dope being processed and the resulting poresize in at least one zone of the three-zone microporous membrane. 11.The system of claim 10 wherein the thermal manipulation means furthercomprises: cooling means, operatively connected to the at least onethermal manipulation means, for cooling the dope after processing by thethermal manipulation means to a temperature such that the dope has aviscosity sufficient for processing by any one of the three dopeapplication means to produce a microporous phase inversion membrane. 12.The system of claim 10 wherein the heating means further comprises:first heating means, operatively connected to the pump, for elevatingthe temperature of at least a portion of the dope to a temperaturewithin about 2° C. below the predetermined temperature; and secondheating means, operatively connected to the first heating means, forfurther elevating the temperature of at least a portion of the dope to atemperature no higher than within about ±0.2° C. of the predeterminedtemperature.
 13. The system of claim 12 wherein the second heating meansfurther elevates the temperature of the dope to a temperature no higherthan within about ±0.15° C. of the predetermined temperature.
 14. Thesystem of claim 1 further comprising: means, operatively positionedbetween the vessel containing the ternary phase inversion polymer andthe dope processing site, for controlling the thickness of the dopeduring applied by the application means.
 15. The system of claim 1further comprising: means, operatively positioned between the vesselcontaining the ternary phase inversion polymer and the dope processingsite, for controlling the coating weight of the dope during applicationby the application means.
 16. The system of claim 1 wherein the motherdope further comprises: a phase inversion membrane polymer, a solventand a nonsolvent in solution.
 17. The system of claim 16 wherein thephase inversion membrane polymer is selected from the group consistingof: copolymers of hexamethylene diamine and adipic acid (nylon 66),copolymers of hexmethylene diamine and sebacic acid (nylon 610),homopolymers of polycaprolactam (nylon 6) and copolymers oftetramethylenediamine and adipic acid (nylon 46).
 18. The system ofclaim 16 wherein the phase inversion membrane polymer consists of:copolymers of hexamethylene diamine and adipic acid (nylon 66).
 19. Thesystem of claim 16 wherein the phase inversion membrane polymer isselected from the group consisting of: polyamide resins have a ratio ofmethylene (CH₂) to amide (NHCO) groups within the range of about 4:1 toabout 8:1.
 20. The system of claim 16 wherein the phase inversionmembrane polymer is selected from the group consisting of: polyamideresins have a ratio of methylene (CH₂) to amide (NHCO) groups within therange of about 5:1 to about 7:1.
 21. The system of claim 16 wherein thephase inversion membrane polymer has a molecular weight, within therange from about 15,000 to about 42,000 (number average molecularweight).
 22. The system of claim 16 wherein the phase inversion membranepolymer is polyhexamethylene adipamide (nylon 66) having molecularweights above about 30,000 (number average molecular weight).
 23. Thesystem of claim 1 wherein, each of the at least three dope applicationmeans further comprises: pressure means for operatively deliveringthermally manipulated dope thereto.
 24. A system for manufacturingthree-zone microporous membrane, the system comprising: at least onevessel for containing a ternary phase inversion polymer mother dope; adope processing site, operatively connected to the at least one vesselcontaining the ternary phase inversion polymer mother dope; a dopetransportation system, operatively connected to the at least one vesseland to the dope processing site, for transporting the dope from thevessel to the dope processing site; means, operatively connected to theat least one vessel, for moving the dope through the dope transportationsystem from the at least one vessel to the dope processing site; atleast two thermal manipulation means, operatively connected to the atleast one vessel, the dope transportation system and the dope processingsite, for transforming the dope into any one of a plurality of differentpore size producing dopes; and at least three dope application means,two operatively connected to a respective one of the two thermalmanipulation means for application of the dope delivered to the dopeprocessing site to form three-zone microporous membrane.
 25. A systemfor manufacturing three-zone microporous membrane, the systemcomprising: at least one vessel for containing a ternary phase inversionpolymer mother dope; a dope processing site, operatively connected tothe at least one vessel containing the ternary phase inversion polymermother dope; a dope transportation system, operatively connected to theat least one vessel and to the dope processing site, for transportingthe dope from the vessel to the dope processing site; means, operativelyconnected to the at least one vessel, for moving the dope through thedope transportation system from the at least one vessel to the dopeprocessing site; at least three thermal manipulation means, operativelyconnected to the at least one vessel, the dope transportation system andthe dope processing site, for transforming the dope into any one of aplurality of different possible pore size producing dopes; and at leastthree dope application means, each operatively connected to a respectiveone of the three thermal manipulation means for application of the dopedelivered to the dope processing site to form three-zone microporousmembrane.
 26. A system for manufacturing three-zone microporousmembrane, the system comprising: at least one vessel for containing aternary phase inversion polymer mother dope; a dope processing site; adope transportation system, operatively connected to the at least onevessel and the dope processing site, for transfer of dope from thevessel to the dope processing site; pressure means, operativelyconnected to the at least one vessel, being capable of producingsufficient pressure for moving the dope in the dope transportationsystem from the at least one vessel to the dope processing site; atleast one thermal manipulation mechanism, operatively connected to theat least one vessel and the dope processing site, for transforming thedope into any one of a plurality of different possible pore sizeproducing dopes; and at least three dope application mechanismsoperative at the dope processing site and operatively connected to theat least one thermal manipulation mechanism, for applying the thermallymanipulated dope at the dope processing site to form three-zonemicroporous membrane.
 27. The system of claim 26 further comprising: atleast a second thermal manipulation mechanism, operatively connected tothe at least one vessel, the dope transportation system and the at leasta second dope application mechanism, for transforming the dope into anyone of a plurality of different possible pore size producing dopes forapplication at the dope processing site by the at least second dopeapplication mechanism.
 28. The system of claim 27 further comprising: atleast a third dope application mechanism operative at the dopeprocessing site; and at least a third thermal manipulation mechanism,operatively connected to at least one vessel, the dope transportingsystem and the at least a second dope application mechanism, fortransforming the dope into any one of a plurality of different possiblepore size producing dopes for application at the dope processing site bythe at least third application mechanism.
 29. The system of claim 26further comprising: at least a second and a third dope applicationmechanism operative at the dope processing site; and at least a secondand a third thermal manipulation mechanism, operatively connected to theat least one vessel and at least the second and the third dopeapplication mechanisms respectively, for transforming the dope pumpedfrom the at least one vessel to the second and the third thermalmanipulation mechanism into any one of a plurality of different possiblepore size producing dopes for application at the dope processing site.30. The system of claim 26 further comprising: at least a second vesseloperatively connected to the dope transporting mechanism, for containinga ternary phase inversion polymer dope, the dope having been exposed toa mixing temperature sufficient to effect dissolution and equilibriummixing of the polymer, solvent and nonsolvent, the vessel and the dopecontained therein being maintained at a temperature sufficient tostabilize and maintain the mixture after cooling from the mixingtemperature.
 31. The system of claim 30 further comprising: at least athird vessel, operatively connected to the dope transporting system, forcontaining a ternary phase inversion polymer dope, the dope having beenexposed to a mixing temperature sufficient to effect dissolution andequilibrium mixing of the polymer, solvent and nonsolvent, the vesseland the dope contained therein being maintained at a temperature beingsufficient to stabilize and maintain the mixture after cooling from themixing temperature.
 32. The system of claim 26 further comprising: abypass mechanism, operatively connected to the at least one thermalmanipulation mechanism, for diverting dope being transported from the atleast one vessel to the dope processing site such that the dope is notprocessed by the at least one thermal manipulation mechanism prior todelivery to the dope processing site.
 33. The system of claim 27 furthercomprising: a bypass mechanism, operatively connected to the at leastthe second thermal manipulation mechanism, for diverting dope from atleast one vessel to the dope processing site such that the dope is notprocessed by the at least second thermal manipulation mechanism prior todelivery to the dope processing site.
 34. The system of claim 28 furthercomprising: a bypass mechanism, operatively connected to at least thethird thermal manipulation mechanism, for diverting dope from the atleast one vessel to the dope processing site such that the dope is notprocessed by the at least third thermal manipulation mechanism prior tobeing delivered to the processing site.
 35. The system of claim 26wherein the thermal manipulation mechanism further comprises: at leastone heating mechanism, operatively positioned in the at least onethermal manipulation mechanism, for elevating the temperature of atleast a portion of the dope to a temperature within about ±0.2° C. of apredetermined temperature, the predetermined temperature being selectedfrom a calibrated characterization curve which describes therelationship between the dope being processed and the resulting poresize in at least one zone of the formed three-zone membrane.
 36. Thesystem of claim 35 wherein the thermal manipulation mechanism furthercomprises: at least one cooling mechanism, operatively connected to theat least one thermal manipulation mechanism, for cooling the dope afterprocessing by the thermal manipulation mechanism to a temperature suchthat the dope has a viscosity sufficient for processing by at least onedope application mechanism to produce a microporous phase inversionmembrane.
 37. The system of claim 35 wherein the at least one heatingmechanism further comprises: a first heating mechanism, operativelyconnected to the pump, for elevating the temperature of at least aportion of the dope to a temperature within about 2° C. below thepredetermined temperature; and a second heating mechanism, operativelyconnected to the first heating mechanism, for further elevating thetemperature of at least a portion of the dope to a temperature no higherthan within about ±0.2° C. of the predetermined temperature.
 38. Thesystem of claim 37 wherein the second heating mechanism further elevatesthe temperature of the dope to a temperature no higher than within about±0.15° C. of the predetermined temperature.
 39. The system of claim 26further comprising: a mechanism, operatively positioned at the dopeprocessing site, for controlling the thickness of the dope duringapplication by the application mechanism.
 40. The system of claim 26further comprising: a mechanism, operatively positioned between thevessel containing the ternary phase inversion polymer and the dopeprocessing site, for controlling the coating weight of the dope duringapplication by the application mechanism.
 41. A system for manufacturingthree-zone microporous membrane, the system comprising: at least onevessel for containing a ternary phase inversion polymer mother dope, thedope having been exposed to a mixing temperature sufficient to effectdissolution and equilibrium mixing of the polymer, solvent andnonsolvent, the vessel and the dope contained therein being maintainedat a temperature sufficient to stabilize and maintain the mixture aftercooling from the mixing temperature; a dope transportation system,operatively connected to the at least one vessel and to a dopeprocessing site, for transporting the dope from the vessel to the dopeprocessing site; at least one pump, operatively connected to the atleast one vessel, for moving the dope in the dope transportation systemfrom the at least one vessel to the dope processing site; at least threethermal manipulation mechanisms, operatively connected to the at leastone vessel, the dope transportation system and the dope processing site,for transforming the dope from the at least one vessel into any one of aplurality of different possible pore size producing dopes; and at leastthree dope application mechanisms, operatively connected to each of thethree thermal manipulation mechanisms for application of the dopedelivered to the dope processing site to form three-zone microporousmembrane.
 42. A system for manufacturing three-zone microporousmembrane, the system comprising: at least one vessel for containing aternary phase inversion polymer mother dope; a dope processing site; atleast one pressure means, operatively connected to the at least onevessel, and the dope processing site for moving the dope from the atleast one vessel to the dope processing site; a dope transportationsystem, operatively connected to the at least one vessel and the dopeprocessing site, for transfer of the dope from the vessel to the dopeprocessing site; at least one thermal manipulation means, operativelyconnected to the at least one vessel and the dope processing site, fortransforming the dope from the at least one vessel into any one of aplurality of different possible pore size producing dopes; bypass means,operatively connected to the at least one thermal manipulation means,for diverting dope being transported from the at least one vessel to thedope processing site such that the dope is not processed by the at leastone thermal manipulation means prior to delivery to the dope processingsite; and at least three dope application means, operative at the dopeprocessing site and operatively connected to the at least one thermalmanipulation means, for applying the transformed dope at the dopeprocessing site.
 43. A system for manufacturing three-zone microporousmembrane, the system comprising: at least one vessel for containing aternary phase inversion polymer mother dope; a dope processing site;pressure means, operatively connected to the at least one vessel, formoving the dope from the at least one vessel to the dope processingsite; a dope transportation system, operatively connected to the atleast one vessel and the dope processing site, for transfer of dope fromthe vessel to the dope processing site; at least one thermalmanipulation mechanism, operatively connected to the at least one vesseland the dope processing site, for transforming the dope into any one ofa plurality of different possible pore size producing dopes; bypassmeans, operatively connected to the at least one thermal manipulationmeans, for diverting dope being transported from the at least one vesselto the dope processing site such that the dope is not processed by theat least one thermal manipulation means prior to delivery to the dopeprocessing site; and at least three dope application mechanismsoperative at the dope processing site and operatively connected to theat least one thermal manipulation mechanism, for applying the thermallymanipulated dope at the dope processing site.